Friday, December 2, 2011

Vagabonding Across the 39th Parallel: Whispers of the Past in Stone

Two tales of serendipity...

Twenty-two years ago, I was leading students on a tour of the Colorado Plateau for the first time. I was following a number of new roads, and I was learning as much on the trip as my students were. We were discussing rock art, the petroglyphs and pictographs left behind by the ancestral Pueblo people. We were driving down a canyon, and I mentioned how the rock art was emphasized by desert varnish, the dark manganese oxide deposits that often coat sandstone surfaces in the desert. I pointed to the first cliff I saw and said "that's the kind of varnish that makes for nice petroglyphs". I hit the brakes, because as I said it, I could see the rock carvings. I would have missed them.

The first petroglyphs that I saw from the highway on the trip long ago were stylized bighorn sheep. We passed by the same place during our vagabonding journey across the 39th parallel in July. We stopped and got out to have a look.
A short distance away we found a strange beastie of some sort. I'm not sure what it was meant to be...perhaps a coyote?
During that trip in 1989, I was having a great time wandering along the cliff looking for other messages in stone. It is a truism that you will find what you are looking for, and miss what you are not looking for. I was watching for carvings in desert varnish and ignoring the lighter surfaces. I very nearly missed the delicate drawings in a high alcove. The pictographs were stunningly detailed and almost hallucinogenic in their symbolism; the central section, composed of three strange figures, is shown at the top of the post. Hummingbirds can be seen flying about the nightmarish beings. I have a hard time getting into the minds of the original artist.
The figures are faded and hard to see; I've had to heighten the contrast a bit to make them more visible in the photos.  I have noticed degradation in the twenty years that I've known of their existence. I hope they can last, being located next to a fairly busy highway (you may notice I'm not being specific about their location; that's on purpose).

One of the things that I like about pictographs and petroglyphs is that they are the traces of a living moment. Archaeology and paleontology often deal with death: bones and shells are the remains of people and animals after life has ended. Rock art preserves an action of a living thinking being.

I feel the same way about paleoichnology (the study of trackways and burrows and other traces of living organisms). Living animals leave marks of their activities in the rocks, and finding these traces gives us a feel for action and movement, not death and decay. The second story of serendipity involved dinosaur trackways.

During our long-ago trip to the Colorado Plateau, I could count the total of my known dinosaur trackway sites on one was a spot near Tuba City, AZ that is marked on all AAA maps. I had come across a paper that suggested that perhaps hundreds of thousands of trackways were preserved along the top of sedimentary layer exposed in and around Arches National Park. We looked at a geologic map of the park, found an old mining road, and set out on a three mile hike in the broiling sun. Our toiling bore fruit...we found dozens of tracks in an isolated outcrop. They were eroded from a contact between a tidal mudflat deposit and a sand dune formation. The tracks were freshly exposed, and clearly would be eroded away within a few decades or centuries. It was a great moment for our students and me.

I was telling Mrs. Geotripper this story as we drove along Highway 191 north of Moab. I was saying something to the effect that any old ranch road branching off the highway probably would lead to a trackway site, and she said "like that one?" I braked and we pulled off onto the gravel access road, and immediately saw the sign in the picture below. The Bureau of Land Management was on the job!
Photo by Mrs. Geotripper
I'm not saying the road was in perfect had been raining and there were a few serious puddles in our way. We gingerly worked our way past the obstructions and parked at the trailhead.
The Copper Ridge site is apparently fairly new. There is a parking area, a very modest open-to-sky toilet, and an interpretive sign.
The trackways are several hundred feet up the hill. The recent downpours had eroded the trail somewhat, but access was not overly difficult. The site is unique in that it preserves a series of tracks made by striding animals. The most obvious had three prominent toes and probably belonged to a theropod meat-eater like Allosaurus.
photo by Mrs. Geotripper
They would be easier to see in the morning or late afternoon when highlighted by shadows. We dripped a bit of our precious water supply to bring out the shape of the footprints.
The other unusual trackway is that of a sauropod that walked through the site. Although the specific species is not known, it may have been a Camarasaurus, Apatosaurus, or Diplodicus, the Jurassic giant longnecks.
photo by Mrs. Geotripper
I later found that the Copper Ridge Trackway site was described in the book Geology Underfoot in Southern Utah by Ornduff, Wieder, and Futey. Ironically, the book was sitting in our backseat while we were driving along, but I hadn't read through it yet.

There was one more oddity about our day. As we walked up the hill towards the tracksite, I realized we weren't alone. There were hundreds of crows swirling in the sky over our heads (in the high resolution photo I counted at least 200 of them). I've seen lots of raven pairs in the region, but I have never seen such a huge gathering of their smaller cousins. Do any of my birder readers have a comment on the flocking behavior of crows in the desert? We have huge murders, or flocks, of crows in the Central Valley where food is plentiful, but in the desert? I was reminded of the Crebain flocks in the Lord of the Rings!