Painted Desert

Painted Desert

Saturday, June 04, 2011

Get the tongs

Last weekend I traveled to Glenwood Springs, midway between here and Denver, to go camping with DP. While there I forced her to cut my hair. We took "before" and "after" photos. Here I am, unhappy, with my mop of hair (which actually doesn't look that bad in this picture, but the problem was that it only looked good about 10% of the time, and when it chose to look good was totally random and I could not figure out how to deliberately get it into that state).
I gave various instructions to DP regarding my hair, the only ironclad injunction being "Don't make me look like Vanilla Ice," but in the end the haircut was her own creation and she did astoundingly well for having no idea how to cut someone's hair, and basically being forced into doing so at scissorpoint.
We then hiked to Hanging Lake, one of the most popular trails in Colorado. It was definitely more entertaining than usual this weekend as there has been so much rain, and there is so much snowpack to be melted this spring, that the stream beside the trail was overflowing and for half of the hike it had taken over the trail itself, requiring creative scrambling on rocks. Here, DP examines the trail (to her left) down which water is shooting... note the water breaking high against the tree on right:
Hanging Lake. We were innocently eating lunch here when a wind whipped up and blew our paper grocery bag out onto the lake, where it could not be retrieved. The 20 tourists who had just arrived had to wait for it to drift away before they could get a bag-free picture of the falls. Whoops.
Back in Utah, the rain has brought out an unusual profusion of mosquitoes, and also wildflowers.
The cacti have absorbed so much water that their pads look like footballs, ready to pop. We will come upon one when hiking and burst into laughter spontaneously because they look so funny, like a small child that has decided to hold its breath. I should get a picture to show you all. I would also like to get a picture of the bird that keeps singing to its reflection in my car's side-view mirror, but it's so hard to get pictures of birds when they're moving.

We are working in the Navajo Formation. I have talked about formations before in this blog, but I don't expect anyone who's not a geology student to remember these things. Though normal people use the words "rock formation" to describe any interesting rock feature ("Look at the rock formations in that cave!"), geologically speaking, the word "formation" has a very specific definition. It is a distinct unit of rock that is mappable over large distances. Here is a picture of three formations in the park, which were originally deposited horizontally but which have been tilted by tectonic activity:
The cliffs on the left are the Entrada Formation (sandstone; this formation forms the arches at Arches NP). The red rock in the center is the Carmel Formation (mostly mudstone) and the light slope on the right is the Navajo Formation (sandstone). They are distinct (you can tell them apart from each other) and mappable over large areas, cropping out in many places over Utah and Arizona.

Generally, the rocks in a formation were deposited in the same environment, but not necessarily at the same time. All of the Navajo was deposited in an erg, or sand sea (like today's Sahara). But this erg may have grown, shrunk, or migrated over time, so that--for instance--the Navajo in northeast Utah may not be from the same time at all as the Navajo in Zion National Park, and they might have different fossils. So formations are "time-transgressive." They also vary in thickness; the Navajo might reach to 200 feet here, but forms cliffs 1,000 feet high in Zion.

There aren't many fossils in the Navajo. Many things must happen for a bone to be found as a fossil; it must escape decay or being eaten or trampled to bits by other creatures, must escape being eroded away by tumbling in a stream; it must be impregnated by minerals dissolved in the groundwater. Eventually the earth's surface must be eroded again so that the fossil is brought near the surface, but not left out too long before being found, or it will be weathered away and lost. Only a handful of fossil sites have ever been found in the Navajo (as opposed to, say, thousands in the Morrison Formation, one of the most famous fossil-producing formations). Not many things live in a sand sea to begin with, and those that do may not have their bones locked away from scavenging and decay upon death, as a creature who sank to the bottom of a lake or swamp might. But there are still tracks and traces. Yesterday we looked at some dinosaur footprints.

Here we are looking at a section of the Navajo that was not built into dunes, but was flat-lying, and where the sand built up in layers containing different amounts of iron-bearing minerals. The layers with more iron "rusted" to a red color. A dinosaur stepped here, pushing down several layers at once, but they have since eroded flat. You can faintly see the red layer, in the shape of a three-toed footprint, peeking out between layers of pale sand. (The toes point downwards.)
Here is another print made in the same fashion, also with toes pointing downwards. It is from a smaller creature and is imperfect, with part of the heel obscured. You can also see some toe- and claw-marks from another print that was closer to my hand.
The study of fossil traces is called ichnology, and I will talk more about it in the future, including what it can be used for (other than filling up blog space).

Last night we played frisbee and one of us got the frisbee on the roof. After a couple other plans for retrieving it failed, I constructed this grappling hook made of two sets of tongs and eventually managed to snag the frisbee with it. That was the most excitement we had all week.

1 comment:

Mom said...

Interesting haircut.

Liked the tong trick.