Posts Tagged ‘Basalt’

Pressure Cooker

Wednesday, July 17th, 2013

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  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.

Topcoat

Sunday, August 26th, 2012

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  Life has a way of inhabiting even the strangest of places. And in doing so, it makes those places themselves come alive, in a bigger way. As any artist knows, it is the small touches that make the larger artwork extraordinary. I was drawn to the pinnacles and cliffs of the desert the first time I saw them. It wasn’t just out of scientific curiosity, or an interest in a landscape different from the one with which I was familiar.

  It was that in many ways, the rocks themselves looked alive. They had colors of their own – yes – but superimposed upon those were abstract patterns and splotches of yellow, orange, green, and gray. And then there were the dripping streaks of brown and black, looking so much like dark chocolate frosting looks as it spills casually off the side of a layer cake.

  In some such places, and when I was alone, I would be still for a moment, let my mind calm, and just take in the view in front of me, without trying to analyze it. Detailed and complicated patterns would appear among the more readily apparent boulders and fractures, turning the scene into a kaleidoscope of colors, shapes, and figures. Jackson Pollock himself couldn’t have displayed more impressive works of art.

  A coating of life is what is responsible for that look – small life creates bigger life, so to speak. Growths of lichens, desert varnish, and moss are the “paints” upon the land. But they are not just “on” the rocks indifferently. They are connected to the rocks – the rocks give them life. Tourists from other climates ask me about the colors and patterns on the formations around the Valley of the Sun. Maybe we take it all for granted, but they notice them right away. I explain that they are living things, and they grow very, very slowly.

  The brightly colored patches and spots that look like “splatter” paintings are lichens. Lichens are actually two life forms living together: algae and fungi. There are many different “species” of lichens; hence there are many different hues and textures. The algal cells are enclosed in masses of fungal filaments, all in compact arrangements that clutch onto barren rock surfaces. The algae conduct photosynthesis and provide the fungi with nutrients, and the fungi provide the algae with protection. Neither could make it on its own in such a harsh environment.

  There is a budding science of lichenometry – the use of lichen growth as an age-dating technique – but it is still in an inexact stage, and there are many factors that influence growth rates. However, in Arizona, when you see a spot of lichen that is, say, several inches in diameter, you can probably assume that it is on the order of a few hundred to a few thousand years old or so.

  Desert varnish (or “rock varnish”, as it is sometimes called) is what we call the dark, surreal staining that cascades down rock cliffs and spires in our area, and it too, takes a long, long time to develop. The varnish is a very thin layer of manganese and iron oxides, together with clay particles.

  But the key to that covering’s existence is a community of tiny bacteria which live on the rock surface, and process the mineral compounds into a protective coating. By sheltering themselves with the minerals, they shield themselves from heat and drying-out, and intense sunlight. The dripping effect (on the landscape) is a result of their having an easier life where water occasionally flows, but desert varnish also coats many rocks just sitting out in the open. They look black and metallic in the sun’s glare.

  Ancient rock art all over the world owes a lot to those little one-celled creatures. Prehistoric humans systematically and artistically pecked through desert varnish on various rock surfaces to produce what we call petroglyphs. The thin, organically-caused patina masks the lighter color in the rock underneath, and it is that showing-through of the rock itself which forms the desired image.

  Moss is a plant that also grows in small communities on rocks, but you don’t see it in too many places in the desert, as it needs more water. Look for it in spots where the sun never shines, and where water can flow periodically. Most of the time it is a dark-gray or black, soft, puffy growth. The time to see it in its glory is right after a good rainfall, when it comes alive again, and is a bright, emerald green in color. It is also much softer to the touch, then.

  All of this life is part of the surface of the rocks. The next story will look at the life inside of the rocks, and, there is plenty of that, too.

Time After Time

Friday, June 22nd, 2012

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  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.

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.”

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  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.

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.

On Cloud 9

Sunday, July 3rd, 2011

Ancient petroglyphs on a basalt boulder in Phoenix, Arizona.

  The first time I walked up the trail on Shaw Butte, I didn’t even notice them.

  It took another trip, and a little exploring, and then I found what I had been looking for: a set of ancient ruins, and some people think, a prehistoric solar observatory. Actually, there is a sign there, posted by the City of Phoenix, asking visitors to respect these antiquities. Just behind a bush, it’s not easily noticeable from the trail, almost as if it had been planned that way. Like, “now that you’ve found this secret spot, please don’t damage it!”

  Just having read my opening lines here, you might already think you know where I am going with this article—another description of some of the Hohokam ruins for which the Phoenix area is famous.

  There is more than that, however, to this saga. These ruins are just part of a bigger picture that I want to present to you. Geology is not just something we study. Geology is something we are. By that, I mean that humans are inextricably connected to planet Earth and are part of its organic evolution.

  Those who think that nature is here for us to use, that it is at our disposal, have it all wrong. We are part of it. We are all one thing.

  For those of you not familiar with which of the peaks around Phoenix is Shaw Butte, you do know it. When traveling down I-17 from the north, it is the mountain on your left as you drive into the Valley of the Sun, just before you get to what we call Central Phoenix. The butte has a grove of tall metallic towers on its summit, and sort of a looming shape that to me has always suggested, “Welcome to Phoenix.” If you drive north on Fifteenth Avenue from, let’s say, Northern Avenue, you will run right into it.

  If you go around to the north side of the mountain, which some would call the “back” side, and look up, you will see a lot of black, rubbly-looking rock. Much of the north side of Shaw Butte is covered with this rock, known as basalt, or here, officially, the “Moon Hill Basalt”. It flowed up and out of volcanic vents around 20 to 15 million years ago. That sounds like a long time back, but actually these are some of the youngest rocks around the Phoenix area. You can see other areas of basalt around the Valley, too, and along the freeway to Flagstaff.

  When you look up at the Moon, the dark areas you see that form the “Man in the Moon” are basalt. Maybe that’s where the name of nearby “Moon Hill” came from.

  Those of you that have studied geology — even just the basics — know the three types of rocks: Igneous, Sedimentary, and Metamorphic. The above-mentioned basalt is an igneous rock, once molten.

  “New thinking” scientists now name a fourth rock-type —”Anthropic” rocks — rocks made, modified, or moved by humans. This new classificatory scheme now takes into account what should have been obvious all along.

  Think about how much of the Earth is covered with asphalt, concrete, bricks, shaped stones, and stones transported long distances (like maybe the counter tops in your kitchen). Even little gemstones are rocks which have been cut and modified by humans.

  We are transforming the surface of our planet in ways that other natural processes have never done, and in record speed! Like coral colonies in the sea which build colossal reefs, humans on their own scale add their signature to the world.

  I sat down in the musty dirt, in the middle of what is left of an 800 or 900 year old Hohokam room to ponder this concept, snacking from a bag of “Corn Nuts”, one of my favorite hiking foods. (Not that I’m really into “going native”, but these are very similar to what the Hohokam actually ate back then — roasted corn. How appropriate.)

  It had rained a few days before, and the desert still had that pungent, “wet-bushes” smell to it. The brittlebush all around glowed yellow in the low sunlight. I was all alone, and it was quiet except for the very dull roar of the suburban city stretching off below — traffic noise, occasional dogs barking, a yelled voice here or there, telling the dogs to shut up. I could see far into the distance, miles of human construction laid out everywhere.

  Black boulders surrounded me. They had been piled up to form walls, and pathways, and some sort of arrangement to guide the learned as to when to plant crops, when to get ready for the colder days of the year, when to celebrate whatever. Spiral petroglyphs had been etched into some surfaces. We will never know the exact purposes of this structure.

  Anthropic rocks. Shapes amidst geology, caused and formed by humans.   Unfortunately, I didn’t have a lot of time to linger there. It was an afternoon hike, just a break from work, and I had much more to do that day. I picked up my pack and walked on, past the summit, through who-knows-what-kind-of-radiation blasting out from the gigantic antennas above me.

  Then I found some more ruins, and an even better view.

*********

  It was when I walked up into another set of crumbling walls, down through an old staircase, and out onto a weathered concrete floor that the concept of Anthropic rocks — rocks made, modified, or moved by humans — really sank in.

Downtown Phoenix, Arizona, from the ruins of Cloud Nine.

  The view of Phoenix was grand. I was standing on a semicircular deck, looking out onto a valley below, filled with roadways and houses, and tall buildings in the distance. It was like an immense green carpet laid out there, the look of a garden amongst the barren rocky peaks.

  I had come across the ridge from the Hohokam ruins I had found earlier, and discovered this!

  I tried for a moment to put myself into the mindset of some Hohokam hiker, out for a day’s stroll from the solar observatory I had just visited. You know, like one of those old “Twilight Zone” episodes, where some lonely traveler rounds a bend in a remote road, only to find himself in some future setting, filled with strange structures, the purposes of which are unknown.

  As such, I tried to let my mind just view the scene, without judging it. In the distance, long silvery objects with wings were lifting up, out, and away from near the middle of the sprawl, while others glided down into it.

  My “Hohokam mind” wondered what had happened to the valley I knew, with its low adobe buildings, vast green fields, and long sinuous canals, rippling with life-giving water. My memories recalled how small columns of smoke rose here and there from the flats — signs of cooking, and warmth. There was no roar.

  It had been replaced by this! So similar, yet, so different in its look. There were long straight streets, the patches of greenery laid out in neat square blocks, and I could still see a canal or two. The fields? They were mostly gone, and gleaming buildings of all kinds were everywhere. There were what seemed like thousands and thousands of metallic objects rolling along on the roadways. I could hear distant sounds from them like I had never heard before, like the buzz of insects, but stronger and lower in tone.

  I snapped back to reality. I had once heard of this site where I stood — it was called Cloud Nine. I was standing on the floor of a classy old restaurant which had been named “Cloud Nine”, and it must have been quite a place before it burned down in 1964. A narrow, difficult road had once brought its guests up to this point high on Shaw Butte, where they could gaze out over Phoenix in style.

  You can see this spot today from I-17, as you drive by the mountain. Standing between what are left of its walls, I tried to imagine being there in days gone by, with maybe Sinatra or Sarah Vaughn on the jukebox, the lights of the city just coming on. At one table sat two businessmen talking up a deal; at another, in a dimly lit corner, a couple plotting infidelity over a couple of drinks. I could almost hear the plates rattling, the clink of glasses, and the sizzle of grilling steaks. They smelled delicious.

  Now, all that is left are these decrepit walls and flooring. If it weren’t for the City of Phoenix Park System, these would be gone, too. But here they have been preserved, not out of choice I presume, but because they are too difficult (i.e., expensive) to get at and remove, the land not being open for commercial development. What a great set of ruins!

  I hope the City leaves them alone forever. They have as much character as the older Hohokam ones, with every bit as much right to stay on the mountain. You just need to look at them with new eyes, that’s all.

The now-deserted deck of Cloud Nine, in the Phoenix Mountains Preserve.

  Though not with the original artwork, of course, the remaining walls are intricately decorated — some actually completely covered — with all colors of spray-painted symbols, slogans, and initials left by those intent on leaving their mark in the world. In their own way, those would-be artists came here on pilgrimages, whether to celebrate some event in their lives, to make some statement, or just to take in the magnificent view. I thought again about the petroglyphs I had just seen, on the boulders, over on the other side of the mountain.

  And here is where it all “clicked” for me — the subject of Anthropic rocks, I mean. I have always been very wary of “development”. I have always looked at the continual encroachment of human structures onto the natural world as a negative thing. And many times it is, to be sure. But here I realized that it is also a natural thing — a part of nature.

  As I said above, we are part of geology. Humans are modifying the surface of the Earth in drastic ways, and in big fashion. Cities, dams, highway systems, and canals are just a few examples. We are changing the nature of planet Earth faster than any other force. Whether in the form of Hohokam observatories or Cloud Nine ruins; whether in the form of ancient Hohokam cities or our modern-day metropolis, we are geology.

  What the Hohokam called their “city” we will never know. It was a human-made work of geology, situated in the Salt River Valley — a patch of structure on Earth’s surface. We call its new incarnation (appropriately) Phoenix — it too, a work of geological change, much more massive. What further will grow here in the future we can only guess about, and I have a feeling our vision will be way off.

  It’s hard to imagine 80 years into the future, let alone another 800.