In the humblest dry wash you can discover small replicas of the glamor-pusses of the Colorado Plateau. It is exciting to find such places on your own. We would all like to be the photographer who first shot the moon's arc through a red-rock arch, but alas, it's a little late now.
People new to an arid land are amazed to learn that the landscape has been sculpted by water. To speak more accurately, differential erosion in alternating geologic layers results in topographies that are fun to look at.
My favorite geology book is a delightful, 65 page brochure, written and hand-illustrated by a geology professor [1]. It is written from the point of view of a landscape lover, not a rockhound or gemologist.
The main ideas are that:
1. Soft, easily eroded rocks leave the usual 45 degree slopes in the landscape.
2. Hard, erosion-resistant layers result in vertical walls.
3. Plateau country has many alternating layers of sedimentary rocks which erode differently, per 1 and 2.
4. Hence postcards.
When a hard layer sits on top of a soft layer, the latter erodes back underneath, undermining the hard caprock on top, which eventually breaks off in vertical chunks. That makes the mesa or butte smaller in area, but not sloped or gradual on its sides.
You needn't be at Monument Valley or Moab to see that. Even our 10 foot deep dry wash has vertical walls. Looking carefully, you can see erosion-resistant conglomerate layers in the vertical sides.
And how birds love to cling to roots sticking out of these vertical walls and hide from the wind. Our dry wash is actually soggy and green, so it makes a marvelous micro-system for them.
Look at how abruptly erosion begins at the edge of the field, in the photo above. There is no limestone or sandstone caprock there, as in the classic mesa and butte country of the Colorado Plateau; it is just a grassy field of dirt.
But notice in the photo above the change in color about a foot below the surface. The top layer is strengthened by the roots of the vegetation. That makes it a type of caprock, and we are left with a miniature landscape that looks like an aerial view of famous tourist places in the Southwest.
There are a variety of shapes that are hard to explain. (The reader/commentator can keep his Freudian analysis to himself, please.)
How nice it was to dig out that wonderful little book while writing this post. I found it charming that he illustrated the book with line drawings. That hearkens back to the 1700's when gentlemen worked as amateur "natural philosophers" and gave lectures to a culture-loving public.
Unlike in our day, a scientist and a poet could probably sit down together, enjoy brandy and a cigar, and discuss the hot topics of the day, at least if the servants were out of the room. If nothing else, the scientists were good at drawing; they had to be. They could at least share that with a poet like William Blake.
[1] Scenes of the Plateau Lands and How They Came to Be, Wm. Lee Stokes, 1969, Starstone Publishing. Lithographed in Salt Lake City. Lith-o-graphed indeed!
