Posts Tagged ‘Igneous’

Pressure Cooker

Wednesday, July 17th, 2013

~

  Pictured above is the inner north wall of Cerro Colorado. This structure is about one kilometer (3300 feet) in diameter, and about 110 meters (360 feet) deep. You can just barely make out our vehicles in this image. They are the small white dots, across the crater, along its rim. A dark lava flow can be seen in the distance.
 

  Just across Arizona’s southern border, on the way to the Gulf of California, lies one of the Sonoran Desert’s most spectacular geologic features – the Pinacate Volcanic Field. Few of the many thousands of tourists that each year visit the party-place we call Rocky Point (Puerto Peñasco to the Mexicans) even know that it is there. That’s a good thing, too, for part of its beauty is its desolation. It is one of the most similar places to the surface of the Moon that you will find anywhere on Earth. Not because of its loneliness, though.

  From the highway to the coast, you cannot see that out there in that barrenness lie a number of impressive craters. Get up in the air, however, and it looks much like what you see through a telescope focused on the lunar landscape. Massive, ring-shaped, and deep, those craters show that the now-quiet countryside was once a pretty violent place.

  Previously, I’ve written about the explosive San Francisco Peak(s) of northern Arizona, towering above Flagstaff, and not hard to miss at all. But the craters of the Sierra Pinacate region of Sonora are not readily apparent until you are right there.

  This area lies within a Mexican National Park – the Parque Natural del Gran Desierto del Pinacate – which also features a sea of sand dunes, lava flows, and a number of volcanic cinder cones. It is not the kind of place you want to venture into light-heartedly, with your passenger car and beach clothes. Take a lot of water – that is some good advice, too.

Basalt lava flows cover valley floors within the Gran Desierto del Pinacate.

  To me, the craters are the most interesting things to see, and these are some really good ones. They are different from craters on the Moon, though, because the lunar ones were formed by impact – asteroid, meteoric. Same with Meteor Crater, near Flagstaff.

  The Pinacate craters were created by relatively shallow explosions in the crust of the Earth. They are a type different even from the volcanic craters and cones of northern Arizona, like Sunset Crater. In “geology-speak”, they are called maars, and these happen to be some especially young ones.

  The Gran Desierto (Grand Desert) is a dry, dry place. Yet, deep underneath the sparse desert scrub that does exist there, is groundwater, or very recently was, apparently. That water occupied layers of rock, in turn overlying lower rock units that become hotter with depth.

  Remember, and I’ve written about this in many other articles as well, that this part of North America is very active, geologically. Earth’s crust is and has been breaking up in this zone, and the fractures run deep. Molten rock can move upwards along those fractures, eventually making its way to the surface, hence the cinder cones and lava flows.

Crater Elegante is too wide<br />
to fit into one picture.

  In the past, here in the Pinacate Field, some of that molten rock moved upwards, and encountered groundwater deposits (known as aquifers). When it did, it converted the water instantaneously to steam – massive amounts of it – and the ground literally exploded outward, creating maars.

  Then, at least in some of the cases in the Parque Natural, those exploded chambers collapsed back into themselves, expanding them additionally into structures known as calderas – gaping holes in the ground. There are at least ten of these maar / calderas in the Volcanic Field.

  It is possible that humans witnessed some of the eruptions. Hohokam relics have been found along some of the erosion surfaces in the area. Studies show that the blasts occurred within the last few million years, and some only within the last few thousand years. Very jagged, black, and barren, the basalt lava formations that you drive by between the craters look like they flowed yesterday.

  As you can see, the starkness of the vista adds much to the otherworldly look of this place, so if you can’t make it to the Moon (and most of us won’t have that chance), you can at least get an idea of the lunar scenery by visiting the Pinacates.

  Breathing is easier there, too.

Pathfinder

Sunday, January 8th, 2012

Ancient petroglyphs decorate a basalt boulder at the Deer Valley Rock Art Center in Phoenix, Arizona.

  Take take a look at the boulder in the picture above. You will notice that it is literally covered with markings and drawings. We call these “petroglyphs”, and they were created by pecking through the layer of desert varnish that coats many rocks in arid climates (as opposed to “pictographs”, which are painted onto rocks). Research has shown that petroglyphs in central Arizona were created between about 10,000 and 700 years ago, by peoples we now refer to as Paleo-Indian, Archaic, and Hohokam.

  But, as those of you who read my GeoStories know by now, there is more than that about them that would interest me. What really arouses my curiosity is why they are there.

  They are found in various places around the Valley of the Sun. But why in one place and not another? There are plenty of rock faces and walls scattered around our area. Some have no markings, and others, like the boulders at the Deer Valley Rock Art Center, just off I-17, north of Phoenix, have hundreds or more. Operated by Arizona State University’s Department of Anthropology, this place alone preserves over 1500 such works of art.

  Here, a trail approximately .25 mile long, leads along the base of outcrops of Tertiary age basalt on the edge of the Hedgpeth Hills. This is some of the youngest rock in our area — only about 15 million years old.

  I first visited this place on a beautiful, warm, autumn day, and it seemed that I had it all to myself. The sweet, dry smell of the desert surrounded me with comfort. I was walking along this peaceful trail, looking up at the cascade of dark rocks from above, when I was startled by an abrupt, booming voice from the chaparral around.

  “Hello, sir! May I be of help to you?”

  Totally surprised, I quickly turned around, and saw a man wearing a ranger’s uniform coming towards me from out of the bushes. He was Native American, or Indian (which is the designation he later told me he preferred), stocky, strong looking, with graying hair and chiseled features, and somehow he just “beamed”.

  He introduced himself, and I could see he was “official” by the badge on his uniform.

  In a very amiable manner, he immediately started dispensing information about the Rock Art Center, its history, and of course, the petroglyphs. But I was still trying to figure out why I had not seen him at first, how I had missed noticing him as I walked along that trail. After all, the chaparral there is not that thick or tall. And it seemed that he just “didn’t fit”; as if he had just materialized on the spot. I even had the thought that he was just posing as a ranger! I liked him at once.

  We stood in or near that same place for quite some time, talking about all sorts of things — his background, American Indians, history, artwork on stone that he produces on the side — it was fascinating. I never even made it to the end of the trail! I had to leave, as it was getting late, and I had another appointment. I apologized for having to end our enlightening conversation.

  Then one thing occurred to me strongly. I felt that I had finally met someone who really knew what the petroglyphs there, and elsewhere, were really about. I mean, what were those Indians really up to with all these drawings? I know, I’ve read all the ideas posited by present-day researchers about the markings being religious art, communication symbols, or maybe just plain graffiti.

  But why, in places like this? Why, in some places and not others? What was it about this rubbly, remote (in ancient times), harsh location that inspired people for thousands of years to spend a huge amount of energy creating all these drawings?

  Finally, here was someone who knew.

  So, before turning back along the trail, I explained to my guide my quandary. Those of you familiar with my other writings know where I am going with this: what is it about the rocks that energized the ancients here?

  “I am searching for that answer,” I pleaded, “and maybe you, being a knowledgeable Indian, and an artist, can tell me.”

  His answer was, to say the least, totally unexpected, and it came without hesitation: “Perhaps, sir, what you are really searching for is your own spirituality.”

*********

  If you want to do some “searching” along your own path, this is one place to begin. Go out there, and see what you feel in this special place. Take the Deer Valley Road Exit off I-17, and follow the signs, going west for several miles. The Center is closed on Mondays, and hours during the rest of the week vary with the season and day. You can get more information by calling 623-582-8007.

Gold Dust

Saturday, December 10th, 2011

The classic view of Superstition Mountain, from the Lost Dutchman State Park, Arizona.

  Let’s talk about gold. Not just any gold, but lost gold. If there’s one thing more appealing than found gold, it’s lost gold. Because that means that the gold – maybe an unknown, vast quantity of it – is still out there somewhere, just waiting to be found. Like fairy-dust sprinkled from a magic wand to vitalize some situation, a dusting of the lure of gold can make a place attract people – those people looking to make it big.

  Sometimes they win; sometimes they lose.

  And sometimes they die.

  We have our own place of temptation right here in our backyard: the Superstition Mountains. For the past century or more, this rugged range of desolate, inhospitable, and yet beautiful rock formations just to the east of Phoenix has drawn countless treasure seekers. The goal? A mysterious cache of gold, or gold ore, or maybe even a mine itself. Who knows which? That’s part of the mystery, and the draw of the place.

  In 1891, one Jacob Waltz, a German immigrant and prospector, known locally as the “Dutchman” (men from both the Netherlands and Germany were then frequently called that in America), died in the Phoenix home of a friend, Julia Thomas. On his deathbed, Waltz described to her the location of a gold deposit of which he knew, deep in the Superstition Mountains. But in his possession then were only a few gold nuggets, and he never had appeared to be a wealthy man.

  Yet, Ms. Thomas and two of her friends, the Petrasch brothers, believed that there was something to his story, and they set out to find it. They spent weeks roaming the wilderness, searching for whatever they could find, which ended up being nothing. Julia Thomas did find a way to capitalize on the Dutchman’s fate, however. She drew up and sold some “treasure maps”, as well as told Waltz’s story to at least one freelance writer, who in turn embellished it even further.

  Hence, the story grew, and multiplied. And so today, there are almost too many “Lost Dutchman” stories of which to keep track. (And remember, it is the gold that was lost, not the Dutchman.)

  There are variations which include Mexican miners (who supposedly originally found the gold), Apache Indian raiders (who killed the Mexicans and maybe even Waltz’s sometime mining partner, Jacob Wiser), high-graded gold ore stolen by Waltz himself from near Wickenburg and stashed in the Superstitions, and even Jacob Waltz having murdered his partner to hoard the gold for himself.

  The wildness of the terrain, the relentless, blazing sun and lack of shade, the dearth of water in the remote desert canyons of the Superstitions, and a colorful cast of crazies, desperadoes, and dream-seekers who have over the years spent countless time seeking out the rumored riches have only added to the luster of the story.

  The details of all these legends and maps do not matter so much as the fact that they exist, and that the story of the lost gold endures – the fascination goes on. Over the years more than two dozen adventurers have lost their lives, in one way or another, while exploring the range.

Looking deep into the heart of the Superstition Wilderness, near Phoenix, Arizona. Weaver's Needle is in the background.

  The derivation of the name “Superstition” is not even certain. One version is that in the 1500’s, the Spanish explorer Francisco Vasquez de Coronado apparently gave the mountains that name, based on the Apaches’ claim that therein lay the abode of spirits, ones who did not look kindly upon intrusion, especially in the name of profit.

  Only a few years after Jacob Waltz’s passing, hard-rock gold was discovered not far from the north side of the range, near what is now the little mining town of Goldfield. Millions of dollars were taken from the ground during the heyday of mining operations there.

  That a true in-situ gold deposit does exist in the Superstitions themselves is very unlikely. As I’ve mentioned in the past, the range (in this case, the western end, of which is to where the legends refer) is built-up of thousands of feet of ancient volcanic ash, fused into thick, resistant layers which today have eroded into a maze of pinnacles, ridges, and gorges. Barren volcanic cinders – now rock – and that’s all. Barren of precious gold, that is, but not of dreams.

A maze of golden canyons makes travel through the Superstitions a true adventure. This view is from along the Apache Trail, aka State Route 88.

  Take a look at the Superstition Mountains from a distance, in the setting sun sometime. If you give pause for a moment, they look yellow, even golden. It’s that would-be coating of gold dust out there that you see.

  That and the glimmer in your eyes.

LandMark

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.
 

Touchstone

Thursday, September 8th, 2011

Basaltic Moon Hill, as seen from Shaw Butte, looking northwest, in Phoenix, Arizona.

  Rocks arouse feelings. All we have to consider are gemstones to realize that. Though they are small, the power they exert on the wearer, or even the bestower, is legendary. You can make the case that a stone’s power is constructed by advertising, using diamond as an example. Or you can look at an ancient stone like turquoise, for instance, and mull over the probable connections the ancient Hohokam people in our Valley made between it and the sky, water, or coolness.

  Big rocks elicit feelings, too, I think, and I mean big rocks that form things like cliffs, hills, and mountains. One of my favorites is the rock known as basalt.

  Not long ago, I was trying to “get a feel” myself for what basalt evokes. I was driving around Moon Hill (pictured, from Shaw Butte), that little ridge that lies just north of Thunderbird Road, on the east side of I-17 and 19th Avenue. My attempts to go up onto it were to no avail, however, as every road was gated. I probably could have waited at a gate, and slipped through behind someone else’s car. But then if asked, how would I explain what I was doing there? “Yes, sir. Who? Me? Oh, I’m just here feeling the rocks.”

  “Rrrright,” would undoubtedly be going through the mind of my inquisitor.

  Melancholy, mild foreboding, and loneliness are some of the feelings I’ve seen in myself around basalt in other places. I had really wanted to go door to door on Moon Hill, from home to home (and I could see some nice ones up on top), and ask people what they feel living there.

  Maybe someday I will get that chance. It has got to be different from what people living on Camelback Mountain (mostly granite) feel, for example, or from what people around Squaw Peak (mostly schist) sense. That feeling would have nothing to do with the view, or the facing direction.

  This kind of thinking is, by the way, off the scale for most geologists. But not all. There are those of us of a scientific bent that are open to the subtleties of nature. As one old saying goes, “the devil is in the details.” So are the good spirits, I think, and much of the beauty. Illustrating this view of nature, the Japanese have ways of classifying rocks that are unheard of in our Western culture, and I have pursued this subject in other writings (see “First Impressions”).

  Basalt (say buh-SALT, not BAY-salt) is a very dark, heavy rock. When molten, it flows easily. It covers many of the hills along what we call the Black Canyon Freeway (I-17) between Phoenix and Black Canyon City. Along the road you can see black rock, sort of “dripping” off the edges of the hills.

  That look is simply the result of the basalt breaking up into chunks and fragments that roll and slide downslope because of erosion. The solid rock itself forms very resistant flat caps or layers on much of the higher ground north of the metro area, creating scenic backdrops such as New River Mesa and Skull Mesa (mesa means “table” in Spanish).

Basalt

  Around fifteen million years ago, deep fractures opened the crust of the Earth in the area north of Phoenix, and from within erupted the fiery liquid that then cooled and now covers Moon Hill. The basalt flows in central Arizona are some of the youngest rocks around us. I know, fifteen million years sounds like a long time ago, but it is not, really. Earth is 4.6 billion years old. Fifteen million years represents just a third of one percent of its history!

  I was curious as to the origins of the rock’s name, which was not an easy subject to track down. Apparently the Romans took the name basaltes from the Greeks, who in turn got it from the Egyptians, and it seems to have meant “touchstone”. Another source I saw attributed the word to unknown African sources. But then, Egypt is in Africa.

  The Hawaiian Islands (not an easy place to feel melancholic, I admit) are made mostly of basalt, as are the plains of eastern Washington State (an easier place to be depressed), the Snake River Plain that runs across southern Idaho, and the dark splotches that we see on our moon overhead.

  It covers the seafloors, and if you drive north from Flagstaff towards Page, you can see great long tongues of basalt, now mostly covered by brush, emanating northwards from the San Francisco Peaks, running for miles along Highway 89. In the back-country on the way to Puerto Peñasco (Rocky Point), in Mexico, are some of the most amazingly picturesque basalt flows I have ever seen.

Recent basalt flows cover the desert north of Rocky Point, Mexico.

  Next time you see some, get out of your car, approach it, spend some time, and see what you think. Or more importantly, what you feel.

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….

Bones

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.

Time is on my Side

Wednesday, November 3rd, 2010

Ferruginous quartzite (dark rocks) in Phoenix Mountains, Phoenix, Arizona.

  When I was young, growing up on the brown, flat Cretaceous rocks of central Montana, I used to fantasize about dinosaurs. It’s what got me into geology in the beginning, I guess. I was taken by the idea that where they roamed was right there, in the same physical space I was in at the time. Just about eighty million years earlier is all. Maybe a Tyrannosaurus Rex had actually walked across the ground occupied by my bedroom!

  People tend to visualize scenes from the distant past as though they were necessarily somewhere else. In space, I mean. But there were alien landscapes right here, just not now. This idea is conveyed in H.G. Wells‘ classic novel “The Time Machine”, now recently made (actually remade) into a movie.

  The movie does horrible justice to the original story, but you get the idea by watching the Time Traveler in his machine, sitting in one spot, with the “hours-days-years” odometer rolling on in a blur. He starts the machine and his journey through time in his laboratory in London. At one point (in the book) he “lands” in a rhododendron garden looking over the River Thames, surrounded by alien structures; in another scene he is on a barren beach in the distant future, watching a dying red sun setting into a future ocean of dead, spent waters. All those scenes occur in the same place.

  Back to Phoenix and now, in which the landscape is far different from way back then, let’s say, in Precambrian time, for example. Take a drive on SR 51, the Piestewa Freeway, where it cuts through the Phoenix Mountains, just to the northwest of Squaw Peak, and you will see what I mean.

  If you are going north, look off to the west (left) just after you have passed the Northern Avenue Exit; if you are going south start looking west (right) about the time you get to the Exit ramp. If you like to walk, you can park in the Dreamy Draw area, and approach this area from one of the trails in the Phoenix Mountains Preserve, a city park.

  About half a mile away, up on the east slopes of those rugged rocky peaks you will see dark brown, almost black areas of broken up rocks and rubble. Some of this rock forms a pointed outcrop just at the south end of that set of hills, and is also visible elsewhere in the Park. There are a few houses (with great views of the Valley, to be sure) to the north of these rocks, near a saddle.

  What you are looking at are the remains of ancient, submarine hot springs — very ancient, and very submarine, from the bottom of an ancient ocean. These rocks have the wonderfully technical name of “ferruginous quartzites” and the hot springs that formed them erupted, seethed, and bubbled about 1700 million years ago, at the bottom of a vast sea whose only occupants were life forms so primitive that you would have needed a microscope to get their names. The hot springs were rich in iron, and those iron minerals give the rocks their current color.

  The Phoenix Mountains are made of a section of the earlier crust of Earth where the rocks were formed in an environment somewhat like that off the coast of present day Japan. If you were to walk from the freeway in Dreamy Draw over to Shaw Butte (about 4 miles), you would be going right down through rock section (now standing on end, basically), that shows the whole evolution of that environment. If you were going to strap yourself into Wells’ Time Machine, and dial up, say, April 10, 1,700,000,000 BC, you had better already be wearing your deep-diving equipment!

  Our planet’s crust is in constant motion. The shapes of the land masses we know today are as ephemeral as the shapes of clouds in the sky. The continents move about relentlessly, literally floating on top of more dense fluid rock below. Heat from deep within the Earth sets huge convection currents into motion, causing continental rocks above to glide about, sometimes crashing and fusing together, sometimes splitting into new shapes, all of it happening all of the time, just in too slow of a fashion for us to grasp easily.

  Our journey through time would take us to the edge of one of these land masses, where heat from the gargantuan convection cell below has broken through, boiling the waters, and creating a primordial soup in which early life prospers.