Posts Tagged ‘Granite’


Friday, September 28th, 2012


  That the native inhabitants of the Americas had a different way of relating to the landscape is without much question. Their sacred sites and temples were placed in special geographic places.

  But what led to such a view? Could it be because that within their culture, they value fitting in with nature, not trying to change it? Seeing yourself as part of something is, to be sure, not the same as seeing yourself as separate from something.

  What we are all part of is a vast web of life that covers our planet. So far, based on the current state of scientific knowledge, it is that web which makes Earth distinct and unlike any other place we know of in the Universe.

  That “coating” of life includes plants, of course, and animals, fungi, and microbes of many kinds. Life lives in the air, in the water, and on the land. And, now it turns out, inside the planet, too. It thrives even in the rocks.

  In last month’s GeoStory™ (“Top Coat” — also in, I talked about life on the surface of rocks. However, that layer pales in comparison with what is underneath.

  Geologists and other scientists are beginning to realize that in what we once thought was barren, lifeless stone, is, in many cases, teeming with microorganisms. Some of those microscopic life-forms are strange indeed, and can feed from the rocks, without needing air or light.

  Sedimentary rocks (which are deposited by water or wind) usually have small pore spaces within. These pores can and many times do, contain water, oil, or gases. It is from this porosity that we pump groundwater, petroleum, or natural gas.

  Other kinds of rocks, by nature of the way they formed, have no pores per se. But they frequently contain fractures of all sizes, and water or hydrocarbons can occupy those cracks, too. Living things – microbes – can occupy them all.

  Various experiments over the past few decades have shown that certain bacteria can flourish in such environments. No sunshine. No fresh air. Sometimes stiflingly hot temperatures. Yet, there they grow and multiply. The only thing that seems to be required in all cases for life to exist is the presence of water. We have lots of that, and we know now that our neighbor planet Mars probably does (or at least once did), too.

  No wonder that space scientists look with intense interest upon such organisms. If they can exist in the rocks here, then maybe they can exist in the rocks of Mars, or other worlds, too. And for earth scientists, such “deep life”, is leading to a new level of understanding of how the world works.

  Based on data derived from deep-drilling projects, the late, brilliant, and controversial Cornell University astronomer Thomas Gold did some calculating. His reasonable estimates indicate that the top five kilometers (about three miles) of the Earth’s crust could contain as much as 200 trillion metric tons of live bacteria. This would be like covering the entire planet with a layer of bacterial organisms one and a half meters (approximately five feet) deep!

  This is more than a hundred times as much living mass (called biomass) as all of the other life-forms (including us) of the world put together! If aliens from another world were studying our planet, they would easily conclude that the rocks are the most alive part of it.

  There are, of course, visible remnants of past subsurface life: coal beds, fossils, tar sands and other petroleum formations. There are metallic mineral deposits which seem to have been “helped along” in their genesis by organic life.

  Professor Gold has even suggested that diamonds come from deep-seated organic materials, and we know today that diamonds must form in an environment at least 75 miles down. If hydrocarbon compounds can exist that far below us, and the rocks are alive, so to speak, then the Earth we all know and love is a very unusual place.

  Perhaps, though I can’t prove it, life gravitates towards other life, and I don’t mean just to eat it, either. Maybe it’s a stretch, but think about it the next time you pull into an almost-empty parking lot, and you park right next to another person’s lonely vehicle.

  The Indians (and to be fair, many other ancient cultures) may have subliminally recognized the existence of places where life was, in effect, somehow concentrated nearby, though not apparent on the surface. Some of those places became special to them.

  Ponder that the next time you are out in the great outdoors somewhere, and “feel alive”. Look around and see what makes that so, and then look down, too.

  It may all be underneath you.

Time After Time

Friday, June 22nd, 2012


  If you look through some of the various articles I’ve written, you might think I’ve got a slight obsession with time.

  And you’re right.

  I do! Sometimes I think the reason I love geology so much does not have to do with rocks per se. It has to do with time — the concept of deep time. It’s something akin to looking into the night sky high overhead and being enthralled by the great distances to the stars — the depth of space.

  They are so, so far away that even with our best technology today, just getting to the nearest (not counting our sun) star, Proxima Centauri, only a little over 4 light-years distant, would take over 120,000 years!

  The depth of time has that same kind of fascination for me, and, for sure, lots of other geologists. “Deep time” is another name (and, I think, a more appealing one), for “geologic time” — those time-spans of millions and billions of years that are so incomprehensible to all of us.

  I’ve mentioned in previous stories that many of the rock formations encircling Phoenix are very, very old, like those around Squaw Peak aka Piestewa Peak (nearly 1700 million years old). And I’ve talked about others that are quite young — the basalt on Moon Hill, for example (some 15 million years old). So where are the ones that are in-between? What is their story?

  It’s simple. Around the Phoenix area, they just don’t exist anymore. This was something I didn’t really grasp when I first moved here, until I hiked up Camelback Mountain. There are places there where you can walk up and put your finger on a thin line which has replaced those missing rock formations — a line representing essentially all the deep time that elapsed during the time they were deposited, and then eroded away.

  You don’t have to take that heart-pounding jaunt up the Echo Canyon Trail, though, to see that line. Just drive around the west end of the mountain a bit. Or you can even see it from Camelback Road, anywhere from 44th Street to say, 56th Street.

  The west end of the mountain, what some people see as the head and neck of the reclining camel (it must have been the heat that got to him!), is formed of reddish sandstone (and conglomerate — a rock made of mixed sand, gravel, and boulders) layers. They are tilted gently towards the west, and they lie on top of coarse-grained granite, which further to the east of there forms the highest part of the mountain.

  The granite also looks reddish here, but that’s because of a thin coating of rust-colored sand grains, loosened from the rocks above, now covering it.

  The place where the two different rocks contact each other is called an “unconformity” in geology-speak. In other words, there was no direct transition from the formation of the lower rock to the other one above it. In this case, that line of contact represents over a billion and a half years of time — time in which many thousands of feet (probably) of younger rocks were deposited by wind and water over the older granite, and then subsequently eroded away back down to the granite.

  Then, on top of the granite, the younger red sandstone formations we see now were laid down by more wind, water, and maybe some really destructive landslides. These layers of stone are approximately 25 million years old. In my photo, taken along the Echo Canyon Trail on the north side of Camelback Mountain, you can see where the line separates the two rock types.

  It runs from near the center of the picture towards the lower left corner. The sandstone is seen in the vertical face. The lumpy-looking rock below the line, or unconformity, is the very old granite. Here, confusingly, as I mentioned above, both look reddish-orange, due to the dusty coating. Far in the background and across the valley, you can see the McDowell Mountains.

  Any of you who have traveled to our spectacular Grand Canyon may have seen another and famous (but unrelated) unconformity. Down by the river, the flat-lying rock formations that make up all those colorful layers visible in the canyon walls are sitting directly on much, much older rock.

  There, that contact is called the “Great Unconformity”, and it is a classic, textbook example, well-known to generations of geology students from, where else, their textbooks, where it is always prominently discussed.

A Fine Line

Monday, May 7th, 2012


  It was late afternoon, with the sun orange and low in the southwestern sky — one of those late December days when the air around Phoenix has sort of a drab look — somewhat dusty, layered, and gray. But it was also the Holiday Season, and I felt a bit like celebrating. I had been looking forward to my drive to this part of the Valley all day, as I hadn’t visited it before.

  Had the main reason for my anticipation been that it was another chance to get out and look at the landscape and rock formations? No, I have to confess. It was the thought of having an ice cold Martini, in the laid-back lounge of the Carefree area’s most elegant resort, that had gotten me going.

  I had just moved to Arizona, and I had read that this particular resort was a place not to be missed. That certainly proved out to be true. Rocks did get in the way that day, however, as they do so frequently in my life. Luckily for me, those interludes always make it interesting. They have a tendency to put things in perspective for me — they separate the little things of everyday life from the things of eternity, or at least the bigger picture, and the longer view.

  I was passing Black Mountain, on its south side. I rolled down the window and tried to get a scent of the cool desert air, but there was none. Being new to Arizona, I only guessed that it must take heat to bring out the smell. The peak loomed high to the left; houses and various structures clinging to its barren slopes, interlaced by tiny roadways that snaked up through stands of tall Saguaro cacti, Palo Verde trees, and Jojoba bushes.

  Not cheap real estate, I figured. It would take a few more dollars in the old savings account before I could put something down on one of those. But the monetary “bottom line” separating me from a life of leisure and afternoons on a deck patio up there somewhere, was not what intrigued me. You guessed it — it was the rocks — and more precisely, a line through the rocks.

  From the south, Black Mountain looks neatly divided in half. The western half is all dark, fragmented rock, and the Saguaros must like it, because there is a thin forest of them there. The other side of the mountain, or its eastern flank, looks like a giant pile of beige rubble. There are fewer of the tall, exotic cacti. Granite boulders abound, and the tan rock is all broken and rounded into picturesque shapes and crags.

  I mentally noted that hiking up that side of the mountain would be a real chore. Making my way on down the road, the division through the rocks stuck with me. I knew right then that I would “get into” the geology behind that granite, which rises above the resort’s lodge, too.

  And that the adventure that afternoon would pay off in more ways than one.

  Why the stark division in those rocks? Why the strong contrast between the two sides of Black Mountain? I knew the hotel’s bar would be the perfect place to ponder those very questions. It did end up taking a little more research, and eventually even a hike up to the summit, to fully grasp it all.

  In other GeoStories™, I have discussed the great antiquity of many of the rock formations around the Valley of the Sun. I’ve also related how the Valley’s mountains themselves, which include Black Mountain, are mostly young — meaning only about 15 or 20 million years old (yes, that’s right, that’s geologically young). They are composed of older rock in much the same way as bricks from old buildings have been recycled and used to create new structures.

  In my GeoStory™, “Missing Time”, I discussed Camelback Mountain, where you can see two formations in contact with each other, the line between them representing a vanished past. In this case, however, on Black Mountain, the line running so neatly up and over its divided summit is a forced contact between two ancient rock types—one literally having intruded into the other.

  On the surface of the world about 1.7 billion years ago, where the places known as Cave Creek and Carefree now lie, sat thick formations of rocks laid down as sediments by vast, ancient river systems. Layers of rock, spewed out of nearby volcanoes, occasionally alternated throughout these. It was the landscape of a continent so old we can only speculate about its outlines. We know, though, that it was moving about the Earth’s surface, as all the continental rocks have done throughout history (and still are doing).

  Along with the movement, and its associated heat and pressure, the rock layers changed their nature a bit (this is called metamorphism). We know them now as slates and phyllites — the geologic names of the rocks of the western part of Black Mountain.

  Throughout the next few hundred million years, with this continental crust literally floating on the more dense, moving, plastic layers below, great crumpling forces caused the Earth to convulse and pulse. The energy drove its crust into long “belts” of distorted rock, that in this case actually stretched over a thousand miles to the northeast.

  This particular period of deformation is called the Mazatzal Orogeny (sounds sexy, doesn’t it?), and during its final throes an extremely hot, fluid body of rock, now described as 1.4 billion year old granite, pushed up and intruded into higher reaches of the older rocks. We see part of that intrusion today, the eastern side of the mountain, on the other side of the line dividing Black Mountain. The two rock formations, and the division between them, exist in other places in the Phoenix area, too, but they’re a little harder to see. They have all been exposed, for us to view now, by recent millions of years of weathering and erosion.

  How nice of those rocks, I thought, for they had once again made my day. That diversion was just what I had needed, and oh, by the way, the Martini was perfect.


Monday, November 14th, 2011

Camelback Mountain, in Phoenix, Arizona.

  Ask yourself which natural rock formation has come to symbolize Phoenix? Which one actually represents our city?

  Most people would say Camelback Mountain. Everyone here knows Camelback. Tourists from afar know of Camelback. And even those who have never been to Phoenix have somewhere heard that name, or read it.

  Rising almost out of the middle of the metropolitan area, it gives personality to our city. Like an actor who works best when able to “play off” of a certain other character, Phoenix has that statuesque mountain. More than just a prop, it is, many would say, the centerpiece of our stage in the world.

  If you are new to the Valley, or have just never noticed, when viewed from the south, the mountain’s profile does bear a resemblance to a reclining camel. You can see the head and neck on the west end, and the higher “hump” of the camel is the eastern part of the peak.

  Now since we are in the American Southwest, a camel would seem to be a figure unlikely envisioned in anything local. But there were camels in Arizona in the 1850’s—they were imported by the US Army, and used briefly for transport. That experiment didn’t work out very well, but since a camel’s association with the desert is almost a primeval thing, a sort of camel’s “essence” remains here.

  Few other cities in the world have such prominent, singular, natural monuments within easy reach. Rio de Janeiro, with its Sugarloaf, is one contender; or Capetown, South Africa, with its captivating Table Mountain. The Rock of Gibraltar certainly comes to mind, but it sits at the gate of the Mediterranean Sea, and is not really in a large city. And Ayers Rock, Australia? Well, it’s out in the middle of nowhere.

  Identity is a key factor in one’s psyche, and identification with landscape goes way back to when humans were just figuring out the world. For ancient Native Americans, the association with landscape was a given—for most of us in the modern-day world it is just a distant memory. But it is lodged deep in our minds somewhere, and without it we might as well live in underground bunkers, or windowless, modular structures without end.

  I feel sorry for space-station colonizers of the future, for they will never know the wonder of gazing up at a big, beautiful rock that can be seen for miles and miles, knowing that it is right in their own backyard, and that they can walk right on up it if they like.

  Although many don’t know it as such, Camelback Mountain is just one of the peaks in what are called the Phoenix Mountains. They cut our city roughly in half, and run from Moon Hill, on the northwest end (near I-17), to Camelback itself on the southeast end. North Mountain, Shaw Butte, Squaw Peak, and Mummy Mountain are some of the other well known prominences in the series.

  The whole group is what is known as a fault-block range. The Valley of the Sun owes most of its general appearance to a particular episode of geologic activity called the Basin and Range Disturbance, which ran from around 15 million years to about 8 million years ago.

  That span of time is a very recent part of Earth’s history, and so our setting is really one of geologic youth. The rocks which make up many of the mountains and features around us are very, very old, but they have just been recycled into the shapes we see now, that’s all.

  During that episode, the crust of our planet here stretched out and broke into pieces which run for miles and miles in more or less parallel orientations. With that activity, and because of gravity, some of those slabs started to settle down, alternating in a fashion with blocks left standing in between— the Phoenix Mountains are one such block. Millions of years of erosion then sculpted that high ground into the picturesque shapes we see now, one of which looks like a very tired camel.


  The Valley’s “look” is very much due to “fault-block” mountains, like the Phoenix Mountains. The McDowell Mountains and the Sierra Estrella are also such ranges. But, there is another significant piece of the story of our setting, though, and that has to do with why our Valley floors appear to be so flat. In this case, I will also use Camelback Mountain to illustrate the point.

Camelback Mountain, from the summit of Squaw Peak, in Phoenix, AZ.

  The second picture here was taken from the near the summit of Squaw Peak, looking to the southeast. In it, Camelback Mountain has a shape very different from that in the first photo, where the “reclining camel” can be seen. In the forefront of this image is a ridge of the ancient metamorphic rocks of the Phoenix Mountains, on Squaw Peak.

  But behind it, you can see a small, level valley filled with the growth of civilization—a patchwork of cross streets lined with houses, buildings, landscaping, light poles and wires, and other signatures of humanity. On a mammoth scale, it looks here so much how like a colony of mold might appear in an old, forgotten bowl of Jell-O still open in your refrigerator, a dish with an uneaten piece of fruit left sticking out of the dessert’s firm surface. The mold relentlessly multiplies against the chunk’s base, ever struggling to breed its way up the sides of the lump.

  Similarly, Camelback rises out of that swale—its profile now a rugged, majestic pyramid— accenting the flatness all around it. The vast Sonoran Desert stretches out in back, for many, many miles.

  This view of Camelback Mountain alone, in my mind, makes the “workout” trek up Squaw Peak worth it. Just drive to the Phoenix Mountains Preserve, north of Lincoln Drive, park in the massive parking lot, and start up. For most, it will be slow going, but you will have lots of company. I have read that this hiking route is the busiest trail in North America, and it will indeed seem that way as you make your way up and down along with hundreds of other people, some young, some old; a few running, most walking, taking in the view.

  So why then, given that Earth’s crust is so broken up by the faults that delineated the Phoenix Mountains, is the surrounding landscape so flat? Shouldn’t we see a wilderness of canyons and gorges, and not the gentle valley floor that so readily harbors life and our comfortable, enviable world of greenery and strip malls?

  It’s that old, never ending story of “what is up, must come down”. Over the past ten or fifteen million years that our friend Camelback has been looming above the down-dropped blocks of rock once attached to its flanks, its slopes have also been eroding on a less exaggerated scale—a little bit here, a little bit there, day by day.

  All that sand, gravel, and clay has had to go somewhere, and where it ended up is simply down-slope in the deep basins surrounding Camelback Mountain, the Phoenix Mountains, and all the other ranges in our scenic part of the world.

  Over those millions of years, all of that eroded material—which geologists loosely call alluvium—has accumulated greatly in the Valley of the Sun and many other valleys of southern Arizona. Between all of the mountain ranges around here are deep, deep trenches. The actual bedrock surfaces of many of these basins are way below sea level, and many are thousands of feet below the surrounding landscape.

  That is why the land, out of which rises Camelback Mountain and the other peaks of the Phoenix area, is so flat. It is like a calm ocean of sand and gravel, barely rippling against the ranges, not revealing what lies beneath. What we see above it are simply the very tips of the mountains, in the same way that icebergs only show a small part of their true mass above the water’s surface, belying the real nature of what is unseen.

  In the case of our Camelback, it looks in my picture like it is separated from the rest of the Phoenix Mountains by the flat area, but “below the deck”, it is not. Down there, and here not too far down, underneath those houses, roadways, and trees, is the bedrock that connects all of the Phoenix Range together. Off to its south, and to its north, the fill material is much, much deeper.

  Thankfully, there is lots and lots of that alluvial fill, and those filled-in basins are wide and voluminous, for they hold vast amounts of groundwater—enough to keep that “growth” of civilization going for decades to come.


  There is yet one more part of Camelback’s story—one missed by even the many hundreds of hikers who ascend its slopes daily: that of its role as an ancient sacred spot, where for centuries humans came to connect with their surroundings, or perhaps disconnect from them.

The Grotto in Camelback Mountain.

  Tucked low into the northern side of the rugged and strangely-shaped rocks of its western end, is a large cavity—a shady, cool cave that looks like it might have been designed as a band shell—a prehistoric amphitheater which even way back then was recognized as prime real estate.

  From inside it, the view to the north expands to include the Phoenix Mountains and Squaw Peak. Yet, there is a sense of enclosure, security, and especially of harmony. It’s not just because you are mostly surrounded by solid rock, offering safe haven from any attacker that might want to sneak up on you. No, it’s the feel of the setting that you notice. It feels rejuvenating.

  Many people are under the impression that primitive peoples thought of caves like this one simply as shelter. I would argue the opposite. The Hohokam people who lived in our valley up until around 1450 CE (current era) didn’t need shelter. They already had well-developed pueblos all over the area, as well as vast farm fields, extensive trade routes, and an elaborate culture. Indeed, they had other uses for such special places—what some would call magical places.

  The Camelback Grotto is one such spot. While standing in it, with the rocky, orange-brown, half-dome shaped ceiling some forty or fifty feet overhead, I couldn’t help but notice a close ridge of similar reddish sandstone and conglomerate a hundred yards or so out in front of the opening.

  The more distant mountains are off to the left—the ridge itself interrupts that background range as a natural sculpture of rounded and cave-riddled rock that looks organic, like a growth blooming up from the flat valley floor just below. That arrangement of rock not only adds to the feeling of the place—it is integral to it.

  The Grotto in the rocks of Camelback Mountain was formed by weathering and erosion. Those relatively soft sedimentary layers on Camelback’s west end have all been shaped by the same processes that also formed the scenic redrock buttes in nearby Papago Park, and in fact, they are part of the same geological formation.

  (The first photograph above was taken from the Papago Park area, near McDowell Road, looking north towards Camelback Mountain. The red rocks and buttes of Papago Park also stick out of the Valley’s alluvial fill—only they are lower in elevation and therefore less imposing. When such smaller formations poke up through the surrounding alluvium, they are called inselbergs.)

  It is possible that some of the opening’s shape has been modified by humans, but if so, not in noticeable fashion. As elsewhere on the mountain, the conglomerate unit contains small to massive chunks of much older, angular granite—evidence that these rocks resulted from very violent forces some twentyfive or thirty million years ago. It is serendipitous that such chaotic stone has evolved into the serene site it is.

  Why above do I say “connect”? Because that means changing a state-of-mind. Why do I say “disconnect”? Same thing: that means changing state-of-mind. It’s the change of mind that counts. The alteration of state-of-mind creates a sense of just being there, being absorbed in the present.

  Ancient Indian peoples looked at the landscape as part of their being, not just as something to utilize economically. It was not outside of them—it was part of them. Landscape exerted force on their daily lives, and influenced them in ways most of us just do not get or understand. Some places had the ability to amplify or modify those forces and influences, and the Grotto is one of those sites.

  The Camelback Mountain Grotto has been known to Phoenicians since around the time our city was established. People then visiting the cavern found and noted artifacts such as decorated, short, cane reeds. There were also lumps of salt, shell beads, small bones, arrowheads, and skyblue turquoise.

  But the reeds were particularly intriguing. They appear to have been ceremonial or ritual objects containing plant material, and were embellished with inked-in figures or marks. Wrapped around the outside of many of them was cloth fabric, and they were often found in bundles of four. Incense? Cigarettes? Who knows? Besides being a spiritual setting, maybe the Grotto was a party place, too.

  More than just a landmark, Camelback Mountain has been a special place for at least a thousand years.

  We are fortunate that it still is.

Turquoise Traders

Friday, October 14th, 2011

Mt. Chalchihuitl, in New Mexico.

  The drive through New Mexico had been long and tedious, and though I was tired, I was also excited to reach my goal. Just a few more miles, I thought to myself, and I’ll be there. This was to be the first of several places I had wanted to visit that are now known to be intimately tied to the history of turquoise in the New World.

  I was expecting the place I had been seeking to just jump out at me. But no, it turned out that it wasn’t that noticeable. Had I not been looking for it, I would have just driven on by, like the thousands of cars and trucks a day that zoom north and south between Albuquerque and Santa Fe, oblivious to the little group of small hills just east of the Interstate — another of those redundantly named places in the Southwest — the Cerrillos Hills. (Cerrillos means “little hills”, in Spanish.)

  Probably not one person in a thousand moving along that asphalt ribbon could have told you that in those barren looking hills is the oldest continuously mined site in North America. Like so many other places in our modern world where remnants of past greatness lie within reach of our everyday lives and yet go easily unnoticed and unconsidered, the Cerrillos Hills and their rich mines once shaped empires.

  The Indians of the Southwest, the Aztecs of Mexico, and later the Spaniards, would all come to know of this place and the treasure it once offered – the mineral we call turquoise.

  The world of gemstones is not just science. It also incorporates economics, psychology, art, and history. Especially history, since without tradition, there would be no real value to what otherwise would be just pretty little rocks. They’d be pretty, sure. But to have value, you have to have agreed upon tradition.

  Sometimes, as with diamonds, that tradition has simply been manufactured. Through intense advertising, for example, De Beers has created a tradition associating engagement, marriage, love, and eternity with diamonds. That very profitable tradition didn’t really exist before the twentieth century. I was searching for something much older, something not created by a marketing department somewhere.

  Turquoise is probably the oldest gemstone known. Its use in ornamentation goes back at least 7000 years. In the Americas, its place in history is vague, but, oh so intriguing. For with the continued evolution of our understanding of the extraordinary civilizations of North America, the history of turquoise is integral.

  That these hills are so unobtrusive serves as a kind of metaphor for the history of turquoise itself in the New World. When people in the Southwest think of turquoise jewelry, what undoubtedly comes to mind are large, clunky, elaborate pieces in which a multitude of blue stones are set into hand-worked silver necklaces, belts, and bracelets. The tourist shops and galleries of Scottsdale, Santa Fe, and Taos are loaded with them — some nice; lots of them junk.

  Most don’t realize that this style of turquoise jewelry is really a creation of the last one hundred and fifty years or so. Capitalizing on metal working skills learned from Spanish and Mexican artisans, Navajo, Zuni, and Hopi craftsmen started incorporating turquoise (from all over the Southwest, and now even Asia and labs in France where it is man-made) into silver jewelry. Railroads opened up the West in the late 1800’s, and the silversmiths’ creations found a ready market in the blossoming tourism business.

  Turquoise has one of those complicated chemical formulas that I was glad I didn’t have to memorize in college — a lengthy notation for hydrated, copper aluminum phosphate. We think of it as a blue stone, but green turquoise does occur also. Its composition is not nearly as interesting as its history, though, which goes way back beyond that of the 19th century Indians. Way, way back.

  By the way, our name for this gem, turquoise, is derived from a French phrase meaning “Turkish stone” — probably a reference to the fact that it was first imported into Europe by way of Turkey — its source in that case being mines in Persia, now Iran. Ancient Native Americans had their own name for certain highly sought-after green and bluish-green stones, turquoise among them. It is thought that also included with these gems were those we now call jade, and even poor quality emerald (remember, no one knew the difference between some mineral species until later science understood that they were different and had developed ways to tell them apart).

  For the most part, the earliest Americans apparently did not distinguish between blue and green hues. Both colors signified the same things: coolness, water, fertility. Within the Aztec pantheon of gods and goddesses, which of course evolved out of more ancient Indian beliefs, Chalchiuhtlicue was the deity of rivers and lakes, springs, and the sea. Her name translates as “She of the Jade Skirt”. Blue-green stones became known as Chalchihuitl, and from the association with water and life, they became symbolic, valuable, and objects of power within the shaman’s realm.

  Sources of the cyan-colored gems were varied, but through time one source became preeminent over all. We know it now as Mt. Chalchihuitl, somewhat centrally located in the Cerrillos Hills, and it is there that extensive prehistoric workings are found.

  For over a thousand years, turquoise mined there was carried vast distances by traders ranging over what became the Aztec empire and the outlying homelands of the Anasazi and the Hohokam. It became a basis for trade throughout the evolving cultures of the New World. Before the Spanish conquest, trade in Chalchihuitl would unite those native cultures in ways we are only beginning to understand.

  The Spaniards later laughed at the Indians’ love of the stone, for they were after what they considered to be treasures of much greater value: gold and silver. For those metals, the sacred mountain was a disappointment.


Ruins at Chaco Canyon, New Mexico.

  Not more than several days walk from New Mexico’s Mt. Chalchihuitl lies an obscure canyon carved into brown, marine sands from the Cretaceous period. Wandering through the warm, tropical woods of those ancient times would have been the most famous of “terrible lizards”. Tyrannosaurus Rex and Triceratops fought bloody battles to the death there, while above nearby beaches soared evil-looking, winged reptiles — their narrow eyes fixated on the surf below, lest some tasty morsel go unnoticed. None of those creatures would recognize the area now.

  As you approach the canyon, its presence is not apparent. The view is one of flat table-lands — a desert of brush and scrub where struggling cattle simply maintain life from one day to the next. Only in the last few moments do you drop down and arrive among towering sandstone cliffs, and only in those last minutes does the feeling of the place supersede what the map portrays in such a dry manner.

  As I drew near the day’s objective, it took me by surprise, and it was another of those moments in life when I “got it”. This place is known now as Chaco Canyon. I literally couldn’t believe my eyes. I had seen pictures of it before, but they obviously hadn’t done it justice (just like my photo accompanying this article will not).

  I had read of its amazing ruins, and the dominance of its role in the Anasazi world of the time. And I couldn’t believe that I had waited so many years to come see it. It had just rained. A late afternoon thunderstorm had rolled through — thunder, lightning, and all — dropping the temperature by at least twenty degrees, and the desert smelled lush, lush. That only added sensuality to the scene, and as the low sun came out, and as the temperature rose again, I stood in awe of the setting spread out in front of me.

  What had possessed the old occupants of the enormous, walled, stone structures now lying there in ruin to build on that spot we will never know for sure. But it is one of those places where I am convinced that the power of the setting itself played a key role. We will also never understand what the residents of those massive buildings intended by living there, or what they called the place.

  But one thing we do know now is that the people of Chaco Canyon dominated the turquoise trade of their time. In fact, they may have been instrumental in developing it, and we also know now that the extent of their turquoise trade reached far into Aztec Mexico, and even to the heartland of the Hohokam civilization in what is now south-central Arizona.

  Present-day research shows us that the Chacoan Anasazi exploited the turquoise deposits at Mt. Chalchihuitl to a very great degree, and by way of a process called neutron activation analysis, we know that the sky-blue and cool green gemstones from the Cerrillos Hills made their way all over the American Southwest.

  Evidence uncovered during excavations at Chaco reveals that turquoise was likely traded for exotic birds from Central America, copper bells, and other treasures. Beginning at around 900 CE (Current Era), turquoise usage among the cultures of the region mushroomed, and this corresponds nicely with the rise and dominance of Chacoan culture. A vast system of engineered roadways radiates outward from Chaco Canyon, and it appears that it became the hub of a widespread turquoise trading network — its political influence even possibly based on the precious mineral.

  In diggings so far, over 200,000 pieces of turquoise have been recovered from the ruins of the “Great Houses” of Chaco Canyon. The Chacoans’ monopoly was not to last forever, though, and by 1300 CE turquoise had become common throughout the Indian communities of the Southwest.

  Was it just that major sources other than Mt. Chalchihuitl had been discovered? Had the Chacoans lost their edge in the trade? Maybe their power in the region had “gone to their heads”, and they had become self-centered and aggressive.

  Whatever the case, something sinister had started to happen. All you have to do is look around the region, even around the Valley of the Sun in south-central Arizona, and take note of where ancient settlements were being constructed — on steep, stark hilltops, on boulder-strewn and cacti-covered ridges, in places where no one in their right mind would build for the view alone.

  If you ever visit such now-crumbling ruins, one descriptive word will instantly pop into your mind: defensive. Were ripples of disintegration throughout Chaco culture being felt far and wide?

  Around 1300 CE the Great Houses of Chaco Canyon were abandoned. The turquoise mines of the Cerrillos Hills were quiet. And the deities of the blue gems of Mt. Chalchihuitl would have to wait for other servants.


  With the demise of the Chacoan Anasazi seems to have come a general unraveling of cultures all over the northern highlands of the Southwest. Those traders of old had lost their political and social control of the region, as well as domination of the turquoise trade. The mines at Mt. Chalchihuitl would never again flood Mesoamerica with the blue-green gem of life.

  The high plateaus and mountains of New Mexico are not the end of the story, though, and I made my way towards home.

  In the 14th century, in the sprawling desert valleys of what is now south-central Arizona another civilization was just coming into its own. We now call these ancient people the Hohokam, which is a modern day Piman (Akimel O’odham) word meaning something like “those who have gone” or “all used up”. (Everyone who lives in the Phoenix area should at least be marginally familiar with their legacy. The city’s name owes its existence to early American settlers who realized the extent of the vanished society, and chose to rebuild on its ruins. Like the mythical Phoenix bird did after death, civilization there resurrected itself.)

  There is a lot that remains unknown about the Hohokam. However, many archaeologists do agree that they had more in common with the advanced civilizations of central Mexico (Toltec and Aztec) than any other Indian culture located in the geographic confines of what is the present-day United States. And the Valley of the Sun had likewise been home to one of the greatest centers of prehistoric civilization in North America, in terms of population.

  By some estimates there were fifty or sixty thousand people living in the area where Phoenix, Tempe, and Chandler now sit. They had devised and built a canal system which utilized around one thousand miles of canals to irrigate a body of land encompassing approximately a hundred thousand acres. That is about forty percent of what Arizona’s modern day Salt River Project now irrigates.

  From around 1300 CE, until their collapse at around 1450 CE, there is no question that the Hohokam dominated the Southwest — in cultural influence, food production, and trade. By some accounts, Hohokam-based traders may have ranged as far as Illinois, the California coast, the Yucatan Peninsula, and the Aztec capital of Tenochtitlan, now Mexico City.

  Agricultural goods, textiles, seashell jewelry, and turquoise would have been among their wares. Turquoise jewelry and carvings, once under the control of the Chacoans, had by this time become widespread throughout the Southwest. New mineral deposits of the gemstone had been found, too. Evidence now shows that turquoise was also imported into the Hohokam heartland from the Chalchihuites area, in Zacatecas State, Mexico (not to be confused with Mt. Chalchihuitl, in New Mexico). Other Hohokam turquoise artifacts have been determined to have originated from mines in what is now southern California, not far from Barstow.

  For decades, archaeologists have pondered the relative lack of turquoise objects among Hohokam ruins, and wondered why no evidence has been found of turquoise production facilities, or mining activity. Given the ancients’ propensity for trading, the sky-colored gem should be more ubiquitous in archaeological collections. What was lacking was the so-called “smoking gun” of Hohokam turquoise trade.

  Within the last decade, a site has been found in southern Arizona that just might be that “smoking gun”. On a remote hilltop, near modern day Tucson, sits the ruins of a place known in present-day Indian language as Na’Naksha’lKihhim — the “Village of the Scorpions”. Here are ruins of above-ground houses, a plaza, and a platform-type mound.

  Here, too, has been found evidence of turquoise processing and finishing, and now-spent mines. Although this particular site seems to have been abandoned while Chaco Canyon still dominated the turquoise trade to the northeast, it shows a clear connection to lands further south and is proof of the Hohokam presence in the turquoise trade. If all is as it appears here, the fusion of the civilizations of central Mexico with the Hohokam comes alive through turquoise.

  It was near sunset, and I stood there next to my idling car in the flat wastes, momentarily stopped on the shoulder of yet another roaring modern-day artery of trade. Wheeled vehicles whizzed straight from one horizon to the other. With every one that passed, a blast and thud of wind shook me and pushed me off towards the chaparral.

  Diesel fumes and automotive exhaust overpowered the nearby sweet smell of warm creosote — fading, then returning after each pulse of traffic. I could see purplish ridges and volcanic rock spires in the distance to the west, the landscape of the Village of the Scorpions, and momentarily, I daydreamed about life in the way-station on a trade route now vanished.

  I’ve noted above that what most people think of, when turquoise jewelry is mentioned, are the big, somewhat geometrical, multi-stoned silver ornamentations of the Navajos and Zunis, and that this style is only a recent invention.

Tesserae-style turquoise and shell jewelry.

  The real styles of the native, older occupants of the Southwest include beads, pendants, carved animal and bird motifs, and pieces composed of turquoise and shell tesserae. Tesserae are like little tiles, and were glued with pine resin to shells or wood pieces. This mosaic type is present in Aztec art as well.

  Pictured here is an ancient piece of turquoise jewelry, in the tesserae-style. This piece is a pendant with a small, reddish, center tile of shell, and measures about 9 centimeters (about 3.5 inches) across. While the pictured pendant is not Hohokam in origin (it is from the White River area in eastern Arizona), it is the closest thing I could find to photograph to show the style. It does date from approximately 1200 to 1400 CE.

  Trade routes shift, civilizations come and go, the world becomes ever more complicated and fast. But concepts of life, fertility, and coolness (especially in Arizona) linger — they remain, as does the stone that has come to symbolize them.

  True tradition never dies. It just changes hands, that’s all.

Geology Upside Down

Monday, May 9th, 2011

Four Peaks,on the skyline east of Phoenix, Arizona.

  Dominating the skyline east of Phoenix and Scottsdale, Four Peaks is one of the most recognizable of central Arizona’s mountains. Locals consider it to be one mountain, so I won’t say “Four Peaks are …”. It’s one of Arizona’s landmarks for which little pondering is required as to how it got it’s name! (In the photo above, Four Peaks is in the distance behind the closer Goldfield Mountains.)

  Geologically, it is a piece of landscape art, and the way it formed is almost counterintuitive. You might think that the four summits we see so easily are big piles of rock that were molded into shape on top of the older, lower slopes. But that would be wrong! The rocks of those four summits were there first. Then the granite below was added.

  How, you might ask, could that be? Well, the makeup of the Earth’s crust is a complicated thing, and is not always what it seems. Geologic time, and the forces that have moved things around throughout the history of the world, always seem to combine to give us an interesting story.

  If you drive out the Beeline Highway (SR87), by the time you are about 15 miles from Fountain Hills you will be near Milepost 200, and you will be looking at Four Peaks on your right (east). Even better, go to near Milepost 204 and turn onto the gravel road marked “Four Peaks”, and you can get a few miles closer. You’ll be able to see that the mountain is basically made of two rock formations. One is a continuation of the bedrock you may be standing on: granite. The other forms all four of the peaks. The dividing line between these rocks is more or less where the slope breaks, just below the notches between the peaks.

  About 1700 million years ago, during what we now call Precambrian time, our area lay on the edge of an old continent — an area probably much like today’s Gulf Coast near New Orleans. All of the sand and muck that came down the big rivers from the interior got dumped into a big basin, like the present-day Gulf of Mexico. There it piled up, got buried, eventually hardened, and was baked into thick, resistant layer or slab — very hard rock we call quartzite.

  Several hundred million years later (not really a long time in geologic terms) the immense forces that constantly reshape the Earth’s surface crumpled the land and its many rock formations from side to side, pushing up great mountain ranges that actually extended all the way over to where today’s Great Lakes are. Geologists give this little event a nicely sensual name — the Mazatzal Orogeny.

  During all of that pushing and shoving a lot of the rock below was very hot. Molten granite, in fact, and here’s where the art work comes in. For whatever reason, in the area of the future Verde River Valley, the underside of the above-mentioned quartzite slab was very unevenly shaped. Maybe it started out that way; maybe it got shaped by the pushing action of the molten rock, pulsing up from below. The result, in any case, was that monstrous chunks of the quartzite now hung down into the granite. Four of them.

  Granite erodes away more easily than quartzite. It breaks down into crumbly rock grains, some of which those of us who hate mowing lawns use for landscaping around Phoenix. So the granite around the four big masses of rock slowly wore away, down, down, into rolling hills and slopes and surrealistically shaped boulders that make the Beeline such a scenic drive.

  The four big peaks towering above the trip to Payson even have a geologically technical name: roof pendants — remnants of a much more vast layer of quartzite; a layer of one-time mud and beach sands and sea-side days gone by.

4 Peaks Amethyst gemstone  These big pendants give rise to little pendants — sparkling, beautiful little pendants in the form of the vivid purple gemstones we call Amethyst, mounted into jewelry (yes, not only pendants, but ring stones, earrings, and all other wearable forms).

  You see, up there on southernmost of those peaks, is one of Arizona’s (and America’s) treasures: the Four Peaks Amethyst Mine. Deep inside the quartzite, and way in the past, networks of fractures formed where quartz-rich solutions grew beautiful quartz crystals.

  Quartz is a mineral composed of silicon and oxygen, and the purple variety is called Amethyst. The crystals are now mined and cut into gems, which in this case are considered to be within the world’s finest grade of amethyst.

  You can even wear one — a little pendant cut from a very big one!

 Author’s note: Besides being very inaccessible, the Four Peaks Amethyst Mine is on private property and is completely closed to the public.

Jewel Box

Wednesday, April 27th, 2011

A pegmatite in the Sierra Estrella, southwest of Phoenix, Arizona.

  Cutting the sky southwest of Phoenix is the jagged, long ridge of the Sierra Estrella — it dominates the Valley of the Sun. Yet, it is less well known to locals than many smaller, less imposing ranges here, and I will bet that most Phoenicians couldn’t even name its more prominent peaks.

  I had just set forth up its southwest-facing side — the side opposite from town — and had just barely started along the trail when I was greeted by fields of glitter along the ground’s surface. Multitudes of bright flashes caught my eyes, making a rich scintillation amidst the chollas, saguaros, and ocotillos growing in profusion along those lower slopes.

  Up to that point, the only thing on my mind had been one thought: what a workout this was going to be. A look up at the high summits above me, one of which was my destination, had convinced me that it was going to be a long, long, sweaty day. Although I was on my way up to one of the less conspicuous points along the sawtooth-like crest, I had heard that this trail was one of the more spectacular hikes in the Estrella Mountains — one not to be missed.

  Reaching down to grab one of the sparkles, I saw right away that it was a flat, shiny leaf — but not a leaf of vegetation. Rather it was a thin leaf of stone — a piece of a mineral known as mica — that was beaming back at me. Its lustrous surface had captured the strong light of the desert sun, throwing it right back into my face.

  And I was delighted with that, as I knew that this mineral, and the way it lay strewn all over there in numerous fragments, meant that somewhere up above me, on those steep, rocky cliffs of the Estrellas, was a pegmatite, an example of a rock formation sometimes known as “Nature’s Jewel Box”.

  Right up my alley, I remember thinking. A hike through gemstone country! A treasure hunt, even. Well, not quite, it turned out, but it was close. All that was missing were the gems and jewels (saleable ones, at least).

  By the time I saw it, I was dripping wet and breathing heavily. I was not sure which smelled more strongly: me (probably), or the pungent, desert brush all around, baked dry by the hot, unforgiving sun. There before me, crowning the mountain, was a great outcrop of quartz, white and glassy, looking like a chunky snow-bank, gleaming with the same sheets of mica that I had seen down in the valley.

  If you want to go gem hunting, finding a pegmatite is a good way to start, for pegmatites are rock formations where gem minerals are frequently found. There are other places in and around the Valley where such rock structures also occur. “Swarms” of them are to be found in the Hieroglyphic Mountains, and even Mummy Mountain plays host to some mineralogically-rich ones.

  Imagine a gigantic body of molten rock, granite in this case, deep in the Earth’s crust. As it intrudes into the rock surrounding it, it forces fractures to run through the enclosing hard stone. Into these fractures flows more molten rock, composed of minerals which are more mobile and volatile — distilled, so-to-speak, off the parent mass.

  This “liquor” of fluid rock then cools slowly into a solid, dike-like pattern of large crystals — a pegmatite. Later, when it gets exposed by erosion, its concentration of sharp, angular forms reveals the mixture of segregated minerals within — in this case, quartz and mica.

  It was these large mica plates, weathered and washed out of the formation, that I was seeing along my route. They make excellent reflectors. But no emeralds or sapphires here. (I had kind of figured that.) Otherwise, there would have been a mine here, probably a very old mine, as pegmatites have been known since ancient times as good places to find large crystals of beautiful and rare gemstones.

  I struggled to the very top of the rocks, where the view was breathtaking. In the distance was the metropolis of Phoenix. I could see its downtown skyscrapers, and several snake-like freeways winding through the Valley’s maze of crisscrossed streets and avenues.

  I recognized Camelback Mountain, readily distinguished by its reddish profile, and beyond I could even see the McDowells and the far-off Mazatzal Mountains. Once more grateful that I’d achieved my goal — this time with the added bonus of some unexpected beauty along the way — I sat there on the immense white, dazzling, hard exposure of almost pure silica, and had the quick thought that it was a wonderful place to get a good, all-around suntan, too.

  A little closer to the sun, and heaven, you know….

Rock and Roll

Monday, March 28th, 2011

Granite boulder in sandstone on Camelback Mountain (note the one-foot long scale), in Phoenix, Arizona.

  The sound of a muffled shriek, coming from the seat behind, made me look ahead.

  I corrected the vehicle’s path instantly, putting it back between the yellow lines, so to speak. Fortunately, we had been going only about five miles an hour. What had happened? Well, it was a quick but typical instance of geologist’s “Road-Cut Attention Deficit Disorder”.

  RCADD is little known among the general population, but well known among geologists.

  It is the tendency to be distracted by the rocks in a road-cut or on nearby cliffs, let’s say, while driving past them. (What are those rocks? Where did they come from? What does their structure mean?)

  It is not the kind of thing you want to have kick in while you are speeding along the edge of a precipice, or on a busy freeway — especially if the geologist is the driver, and you are the passenger.

  In this case, I had been driving some tourists from out-of-town down one of the pretty little residential roads high up on the south side of Camelback Mountain.

  We had been looking at marvelous views of the valley, peering through people’s back yards and over rooftops, at South Mountain in the distance, the Sierra Estrella, and the groves of downtown skyscrapers sprouting out of the layer of brown murk that was no doubt at that very moment causing the eyes of the down-towners to itch and burn.

  We had rounded a bend, and that is where I saw it. There, just behind a Palo Verde tree, at eye level and only about 15 feet away, was a giant boulder of very old granite about three feet across, rounded along most of its edges, suspended in the midst of the red sandstone that make up the cliffs that tower above the glamorous homes of the neighborhood we had been invading. That was when RCADD had hit me.

  To the non-geologists next to me, and in the back seat, the puzzle hadn’t registered. After I had adjusted our trajectory, and everyone had breathed a sigh of relief, I explained why I had become so distracted.

  Here was a classic geologic anomaly. How is it, that this big rock could have been deposited right down into the depth of the fine sand? Think about it. Sand like this is usually laid down by relatively slow moving water, or maybe even wind, as in sand dunes.

  How did the heavy boulder get carried into this setting, and just dropped off, before being buried by even more sand? And keep in mind that whatever happened here happened about 25 million years ago — it’s not just evidence of an accident yesterday by one of the construction crews finishing off someone’s million-dollar back patio!

  That one boulder is to me the most curious example of a type of strange geology you can see in several places around Phoenix. The west end of Camelback Mountain, and the buttes in Papago Park are the best places to see these rocks whose formation stretches my imagination, as well as that of other geologists.

  One current theory ascribes their genesis to “long runout landslides”, also known as “sturzstroms”. Maybe in an instant, on a nice summer morning much like today, by a process not yet well understood, a monstrous amount of sand and rock collapsed from the steep slopes of mountains that stood just east of the present- day metro area.

  A vast mixture of rock, sand, and debris rolled out over the flats, at first glance possibly looking much like one of the big dust storms we see during the monsoon season here in Phoenix, but devastating beyond comprehension.

  The landslide flowed for many miles, basically along a layer of air, and then it just stopped dead in its tracks. The theorized mechanism behind such a phenomenon is given the name “acoustic fluidization”.

  Hard to believe? Yes. I kind of want to see one before I can really buy into this theory. There are some modern-day cases of smaller events, however, that seem similar. One happened during the large 1959 earthquake near West Yellowstone, Montana.

  There, at a place just below Hebgen Lake, a mountainside collapsed, flowed instantly down and across the small valley, even running part-way up another mountain on the other side of the river. That landslide obliterated a campground, at once killing 28 people, who in their sleep never knew what hit them.

  You can see some such unusual rocks just by looking out the window as you drive along McDowell Road between the Papago Buttes. You will see large (and small) chunks of granite caught up in reddish sandstone, like dried-out, jagged bleached plums in rusty, desiccated pudding.

  If you spend more than a few seconds looking, watch out! You, too, have RCADD.


  You can see other scenes of rocks, and discover more of our area’s fascinating geologic story by going to a map called “The Rocks of the Valley of the Sun”, where you can click on “Camelback Mountain” to begin a series of pictures.


Tuesday, January 18th, 2011

Surrealistically shaped ancient granite looks

  “How did these boulders get stacked up this way?”

  The tourist who fired off that question to me was impatient, but in a friendly way. We had just started up a trail that wandered over and through a small mountain of weirdly-shaped rocks. Below us lay lush carpets of green, lazy golf courses winding through even more rounded, but smaller, boulders.

  The look from above was that of a carefully tended garden, with tall cacti, Palo Verde trees, and ocotillo everywhere. Bushes surrounding us filled the air with the pungent, sweet, tarry smell of creosote. The warm autumn sun created shadows on the rocks that only accented their beguiling nature.

  Those with me were wearing shorts, tennis shoes, and polo shirts, casually outfitted for the little hike we were on, all eager to learn something about the place to which they had come to escape for a short while the brutal weather back home. Down by the resort, we could see some men that appeared to have just stepped out of a Wall Street office building, looking very smart in their $3000 suits. New arrivals, we all knew. That manner of dress wouldn’t last long. Behind the lobby area there were others wearing not much at all: beautiful people lounging around the pool, margaritas in hand. There were several girls that were …..

  Oh, yes! Back to the rocks.

  The lady was anxious for an answer. She had been pondering an explanation since she had first arrived at the resort several days earlier and had seen the magnificent display of rocks looming above the luxurious lodge. “We don’t have anything like that back home,” she said hurriedly, and then started spewing out what she thought might be possible answers to her own question. “Glaciers did it!” “No?” “Floods?”

  I get asked that question a lot, even from people that live in the Phoenix area, who have grown up around the picturesque granite boulders which provide the exotic backdrop in places like Carefree, Troon, and Reata Pass.

  People’s fascination with them might have something to do with scenes of landscapes remembered from childhood — like maybe from those western movies where outlaws hid amongst such rocks before ambushing the stagecoach. Apaches disappeared into such settings with the cavalry in hot pursuit, and they appear even in scenes from other planets, like the Star Trek episode where Captain Kirk and Spock do battle with an ugly space monster deep within a wilderness of granite shapes and spires. There is something about them that suggests an alien quality.

  But they are not so alien. In fact, in some ways they are the very core of our landscape. Once, I read about an exhibition in New York City, a display of Chinese carvings and garden art in which stone is the central theme. In that show, rocks were called the “Bones of Earth”, and I can think of no more apt name for them here. As we all can see, the landscape of Phoenix is one which has been scoured and eroded by the desert climate right down to the stone within.

  The granite so exposed around here is very old — about 1400 million years old. It intruded into ancient mountain ranges back then, as a molten mass rising from below, squeezed and reshaped by forces on a continental scale. It never made it to the surface, but cooled slowly, slowly. The evidence of this is seen in the large crystals that can be seen just by breaking a piece of it open.

  Later, over the more than one billion years that followed, it became laid bare at the surface. Changes of tension in that process led to fracturing of the rock in many different places and orientations. If you study an outcrop from a short distance, say near The Boulders Resort in Carefree, or the Four Seasons Resort near Pinnacle Peak, you can see that many of the large cracks running through the granite are somewhat parallel to each other. Some run almost horizontally, some run almost vertically, some are diagonal to those.

  The important thing is that they intersect in various places, and when they do, they isolate off chunks of stone, many of which are house-size pieces. As weathering works its toll, the cracks widen out, and sharp corners tend to round out.

  It’s what causes that “stacked” look. They are not piled up at all, like they appear. No glaciers, no floods. It is the way solid rock is breaking down into pieces. Granted, some do eventually roll down-slope, and probably every few thousand years one makes a pretty good “thud”.

  They make for some of the most striking scenery in the world — a setting for which those visitors from Wall Street don’t mind paying to experience.


  You can see other scenes of these formations, and discover more of our area’s fascinating geologic story by going to a map called “The Rocks of the Valley of the Sun”, where you can click on “Black Mountain”, or “Pinnacle Peak”, to begin a series of pictures.