Posts Tagged ‘Petroglyphs’

Name that Tune

Thursday, February 9th, 2012

  I moved to Phoenix about thirteen years ago, and as I drove around a bit back then and started learning my way around town, I took note of the various landforms surrounding us. I couldn’t quite put my finger on why, but South Mountain looked distinct to me — different from and more rounded than the other mountains that stick out of the relentless grid of asphalt and concrete that stretches on and on through the Valley of the Sun.

  I started looking into the reason, and one of the things I soon found out is that the rugged barrier at the south end of Central Avenue is correctly called the South Mountains (note the “s”). Where all the TV towers stand, and what most people refer to as “South Mountain”, is more properly named the Main Ridge. Looking south from the downtown area of Phoenix, you can also see a separate, smaller high point on the west end (right) of that rise. Its correct name is the Alta Ridge. Much lower, in front of it, and just next to the small town of Laveen, is the North Ridge.

  Speaking of names, the Pima Indian (Akimel O’odham) name for this set of peaks is “Muhadag Du’ag”, or “Greasy Mountain” — a take-off on the dark sheen of the rocks there, caused by a surface coloration known as “desert varnish”. If we really wanted to honor Native Americans, especially those who actually lived in the Valley, we would return its name to what they called it. We could have applied this line of thinking to certain other mountains around Phoenix as well, but I’ll save that discussion for another time.

  More often than not, like everyone else in town, I also call this aggregate of lumps South Mountain. The big point here is the way it looks -a long, low dome-shaped rampart. There is one simple reason for that: the rocks of South Mountain were pushed up, basically through the crust of the Earth. Most of the other ranges around us traverse central Arizona for the opposite reason: the landscape is being pulled apart on a massive scale. They are left standing as evidence of that strain as the valleys between them, like our own, drop away slowly, surely over time. Gravity never sleeps.

  South Mountain is what is called in geology-speak a Metamorphic Core Complex, and I’ll spare you some of the technical details. That term, which from now on in this article I’ll refer to as “MCC”, is a great name to throw around at cocktail parties, and one to remember if you are ever to be on one of those TV “Question & Answer” shows with big prize money. There is a whole, albeit small, subset of humanity out there that seems to be fascinated by them, and they’re not just geologists.

  Don’t ask me why, but one time, on a whim, I typed the term into a music-sharing website, and was amazed that a song actually came up with that name. Somebody (artist unknown) had in fact named a song to honor one! I downloaded it immediately, of course, certain the musician would not have minded. It is a spacey-sounding instrumental (naturally, and gladly) — I am not sure what kind of lyrics you could put to the subject of plate tectonics.

  There is “belt” of MCC’s across western North America, running from British Columbia down into Mexico. They run right through central Arizona, and South Mountain is one of the best of them. They are thought to represent an early phase of the “pulling apart” of North America. Around 25 million years ago, the crust started to stretch in a northeast to southwest direction. As it did so, it thinned out, and lighter rocks, which were once more deeply situated, basically “bobbed up” (the pushing-up I mentioned above) as sort of dome-shaped wrinkles — the South Mountains are one such dome.

  Then, millions of years later, the crust actually started to fracture and break apart. As you might expect, the resulting cracks — called faults — run perpendicular to the orientation of the stretching. This force, then, gave us the big valleys we inhabit, and left in-between massive blocks of rock standing — these are the mountains (Camelback Mountain and Squaw / Piestewa Peak, for example) around that have weathered into jagged summits with a character unlike that of South Mountain.

  I am continually perplexed by the number of Phoenicians who have told me they’ve never been up onto the South Mountains! There is no better view of the Valley than what you can get from Dobbins Lookout (the most popular spot). When you go that viewpoint, look just to the east, at the canyon wall just below you. There you will see the rocks all stretched out, horizontally, with very gentle curves from side to side — visible testimony of the doming forces that created the South Mountains MCC (see photo). Once you see that evidence, you will notice the same rock fabric everywhere around in those peaks.

  For more on MCC’s, look at a string of six photos beginning with a view of Central Phoenix from South Mountain. The fifth view in the sequence is a view from the Space Shuttle Atlantis, looking directly down onto the subject of someone’s favorite song.

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.