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Facets of the Natural World around Us ....
June 11th, 2011
You’ve all heard it before. You know, the line about how tough things are, the line about an impossible situation, about being “between a rock and a hard place”.
It was a warm spring day, and I had just about had it with the climb up a steep, brushy, wooded slope, if you want to call it that. It was more like a tangled obstacle course, except that it seemed nearly vertical, and the loose soil beneath my feet made getting up through it even more frustrating, as it was two steps forward, slide back one.
Annoying little bugs swarmed around my face and ears, but they kept me company and gave me something to yell at. They were the only creatures, I’m sure, that would have thought my sweat- soaked shirt and hat smelled nice. I was beginning to wonder if it was worth it, if all this work made any sense. It would be easier to turn around, and go back to the car, now miles down the deep canyon. My heart was pounding. I was trying to find some ruins.
I was well into the rugged Sierra Ancha (in Spanish, “wide mountains”), about 75 miles northeast of Phoenix. This remote range is one of the least explored archaeological areas in Arizona, and it is not hard to understand why. Deeply-incised canyons cut through massive layers of rock, and these in turn are coated with all kinds of thick vegetation – tall pine woods at the summit, right on down to the cactus-strewn canyon floors.
Rattlesnakes abound, and who knows what other dangers, too – maybe the emotional ghosts of those who lived here and built my goal about 700 years ago. Whatever caused people to live in such a place must have been an intensely emotional thing, and I imagine that that emotion was fear.
And then I saw them. Right above me was one of the most spectacular sets of cliff-dwellings I had ever seen, there literally clinging to the massive rock cliffs above. They looked like they had just grown there, right out of the stone. My mind flashed on the connection between life and rocks, and here was another example. Only here it was humans that grew this place in the rocks, and I knew there were more such spots around that area, too. The rocks offered protection.
The Sierra Ancha are so rough and craggy because most of the rock there is very hard and tough, and consequently very resistant to erosion. In the area of these Anchan Culture cliff-dwellings, quartzite and limestone are the order of the day.
Quartzite is a metamorphic rock, meaning that the original stone has been changed by heat and pressure, in this case altering an old sandstone formation (left-over beach sands, possibly) into a much more durable rock unit.
Limestone is a rock, also very unyielding, precipitated out of oceanic waters, and forms vertical cliffs in a lot of places where it occurs.
Both of these rocks point to a time when this part of what we now call Arizona lay along the shores of ancient seas lying to the west and south. It was not North America then, and what we now see as our landscape would then have been around a billion years into the future.
These rocks are collectively known to geologists as the Apache Group. Higher up in their section, you can also see layers of dark basalt, a volcanic rock that erupted way back then in various places, as the old setting went through some convulsive times.
Equivalent rock formations are found in and below the bottom of the Grand Canyon, and there they are approximately 5000 feet lower in elevation than they are here, there near the Colorado River itself. Therefore, the rocks above that point, most all of those colorful layers now seen in the walls of the Grand Canyon, were once on top of the Sierra Ancha as well.
Because of massive uplift of the region, the younger rocks are now gone, and the innards are exposed.
You can see these same rocks when you wind your way up State Route 288 (also known as the Young Road) from the valley floor, near the Salt River and Roosevelt Lake, to the upper reaches of the Sierra Ancha, near Aztec Peak, on the way to the small town of Young. In this stretch, you are going up through time.
My distress at the sweaty work-out turned to delight; my desperation turned to awe. Tough places, tough rocks, I mused. The Apache Group is still there because it is so hard to get at, and in turn, the dwellings of the ancients remain tucked within its depths, mostly untouched, for the same reason.
That the inhabitants of these ruins chose to live, and die, between the difficulties of the nearly impassible terrain below and the sheer walls of stone, demonstrates the incredibly fine line of life to which they clung, and the tenacity of nature itself.
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Tags: Anasazi, Archaeology, psychoGeology, The SouthWest
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May 15th, 2011
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.
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Tags: Earth & Evolution, Phoenix Mountains, Valley of the Sun
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April 27th, 2011
Rocks aren’t the most outgoing of creatures. Silent and stalwart, they don’t make friends easily. Many times they hide behind a facade of trees, shrubs, lichens, and weathered discoloration. And even when seen, their public profile belies their true standing in the world of nature. That profile is what you see at first glance, and what you may be used to seeing each day you pass them by, but, just take a long, closer look, and you might be surprised at what you find staring back at you.
Take the Phoenix Mountains, for example. They’re the range that roughly slices our city in half, and lots of people here don’t even know that that’s their name. They recognize the landmark peaks, though: Camelback Mountain, Squaw Peak, Shadow Mountain, North Mountain, and Shaw Butte, to name a few.
Barren and rugged, they loom above the houses, streets, and freeways of Phoenix like sentinels of antiquity. And for the most part, the rocks there are very old. Except for some dark, almost black rocks at their western reaches (e.g. Moon Hill and parts of Shaw Butte), and the reddish rocks of the Camel’s Head on the western end of Camelback Mountain, they are really old – about 1700 million years old. I’ve talked before about them somewhat before, in an older GeoStory™, called “Time Travel and other Everyday Things”.
But they are not all just one thing, or one kind of rock. They tell us a whole story, and the above age figure is just a reference point. Their genesis spans a lengthy interval of time. For example, probably as much time as has lapsed between now and the end of the “Age of Dinosaurs” (approximately 65 million years) is represented in the rocks between 7th Avenue and the SR51 Freeway – and that’s just the time in which they were formed, not since then.
When you look up at the Phoenix Mountains from Central Phoenix, let’s say, you see an unevenly serrated profile. Let’s just examine one section of that range. Pick out where Central Avenue runs into North Mountain, and then scan over to just beyond where the 51 Freeway cuts through the low pass in the peaks.
Rocks on the left (western) end of that section are much older than the rocks exhibited at the right (eastern) end. We can say it that way because they are all standing on end here, like books standing upright in a bookshelf. They grade from old to younger, as we progress to the east.
At one time, when they were formed, they laid roughly flat, with the western ones underneath the progressively upward younger ones, in this case like a stack of books lying flat on the bottom one. Things have gotten jumbled up a bit since then, however, as the Earth’s outer layers are in part like a hot plastic, capable of being stirred and bent.
My inset graphic here shows just the principle of the stacking – it is not to scale, and the colors do not denote the real, more complicated layers.
Because of their mineralogical makeup, we can determine how rocks were formed – by what processes they came into existence – and therefore determine the environment in which they originated.
Specific minerals in the rocks can then change under different conditions of temperature and pressure, indicating another later environment. All of these factors reveal their life story, and their unique place in the history of the world.
If you were to walk along the easy hiking Trail #100, in the Phoenix Mountains Preserve, from the beautiful new North Mountain Visitor Center, just off of 7th Street, over to the pedestrian tunnel beneath SR51, and through it to the parking area in Dreamy Draw just beyond, you would be walking forward through geologic time.
You would be walking from an ancient deep, seafloor environment, then punctuated by fiery eruptions, right up through a shallower, oceanic setting, and on up into the makings of a prehistoric landscape of river deltas and floodplains.
Had you made that journey back then, so to speak, at that point you would probably have emerged into a scene of towering volcanic peaks, and a desert-like panorama much more stark than today’s.
It would be similar to walking up from the depths of the Indian Ocean in today’s world, onto the beaches of Sumatra, except that no trees, plants, or animals would be there to soften the view. It would be a desolate vista of rocks and sand along the shore, and you would feel very, very alone.
Fortunately, it’s not that lonely today, and you will likely see many other people out hiking if you take that route. They will all be walking one direction or the other, up or down “through time”, most of them oblivious to the story long kept quiet in the rocks all around.
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Tags: Camelback Mountain, Earth & Evolution, Phoenix Mountains, The SouthWest, Valley of the Sun
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March 8th, 2011
Geology, for the most part, is a s–l–o–w process.
A grain of sand moves here, a rivulet develops there. Case in point? I have been walking up and down the same picturesque pile of granite boulders in Carefree, Arizona, for 12 years now, and they still look just the same as they did when I first started those hikes.
But every so often, something wild happens on the Earth, and the terrain changes very quickly and markedly. As with an earthquake, for example. Or with a volcanic eruption for another. Then people’s heads raise, and they take note. If it only was all so exciting.
In our part of the world, both kinds of geologic events have taken place – many times – but it is the volcanoes that have shaped the landscape in the most sensational fashion, and given us so many “Arizona Highways” type memorable scenes and photographs.
One volcano, in particular, stands out above all the others, literally. We know it as the San Francisco Peaks (yes, plural, to most), but it is really one volcano that has erupted a number of times. It forms the dramatic backdrop to Flagstaff, gives Arizonans a place to go skiing in the winter, and can be seen from most all of the northern part of our state. For the Indians, it is a sacred mountain, and a legendary landmark. At 12,633 feet in elevation, it is the highest point in Arizona.
Humphreys Peak, Agassiz Peak, and Fremont Peak are the names of the major summits in the San Francisco Peaks, but they should all be lumped together and called San Francisco Mountain, for it is one thing geologically – a stratovolcano.
It should have a nice conical shape, like Mt. Fuji in Japan, or Vesuvius in Italy. Mt. St. Helens in Washington State also once had such a symmetrically pleasing profile. But then, it blew its top. And now, when viewed from above, it looks “U” shaped and crater-like.
The eruptions that formed San Francisco Mountain began around 1.8 million years ago. That is very recent, relatively speaking. It is after the Grand Canyon was mostly formed, and about the time the latest round of ice-ages was beginning. From the flats of the Colorado Plateau spewed molten rock, in different phases, slowly building towards the sky, sometimes violently, sometimes lazily.
And that, you see, is why it is called a stratovolcano, or sometimes, a composite volcano. It has layers of different kinds of volcanic rock within it, each layer resulting from a separate eruption.
Not all molten rock (called magma) is the same. Some is very fluid when it erupts to the world’s surface, and flows readily. It forms broad, dome-shaped mountains like those of the Hawaiian Islands, or the White Mountains of eastern Arizona, and is called basalt.
Another type of molten rock explodes violently when let loose, and literally blows its confining mountain mass to pieces. That kind is called rhyolite, and such an event in historic time was the 1980 eruption of Mt. St. Helens.
There is whole range of other rock types between these two ends of the volcanic spectrum.
Our own San Francisco Peak blew its top off some 400,000 years ago. The evidence of that is the so-called “Inner Basin”, on the northeast side of the Peak. Humphreys Peak, and the other above-mentioned summits are just the high spots along the rim of the remaining crater of the blowout.
Before that explosion, the summit of San Francisco Peak was probably 15,000 to 16,000 feet above sea-level. Had it not erupted like it did back then, Flagstaff would have had an even better and more spectacular setting, the mountain would have shown a conical profile even higher than the Northwest’s Mt. Rainier, and the skiing would have really been something else indeed.
Volcanism in Arizona is not necessarily over, and in fact, I would bet on that.
The last volcanic eruption in the state took place in 1064 AD, and produced Sunset Crater, a small volcano just to the east of San Francisco Peak, on the east side of Highway 89. This date is known from tree-ring studies in the area, and there is a very good chance that the resident humans of the time witnessed the eruption. Once again, in geologic terms, a thousand years, or even 400, 000 years, is not a long time ago.
To the north, east, and west of Flagstaff are many other volcanic peaks and lava flows, all indicating that somewhere down below, not too deep, there is still plenty of molten rock waiting to burst forth.
Fortunately, with modern technology at our disposal, the chances of an unexpected blowout are very small.
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Tags: Arizona, Colorado Plateau, Earth & Evolution, Flagstaff, Sedona
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