Ranger Kathryn's Arches

April 15, 2010

Lower Courthouse Wash Rocks

Our shady lunch spot along Lower Courthouse Wash

I’ll let you decide whether “rocks” is a noun or a verb in the post title. Either way, I was fascinated on my hike there today. This is a main drainage in the park, and apparently does not dry up. Cottonwoods and willows occupy the wash, and so do nesting raptors. We were there to locate nests for Cooper’s Hawks, Red-Tailed Hawks, and anything else we could find.

(A) Desert Varnish

The red rocks won’t leave me alone. I find them beautiful and mysterious and solidly comforting. The stripes (A) on these rocks are iron oxide and manganese oxide deposits, accelerated by run-off, taken from blowing sediments in the air, adhered to the rock surface by bacteria. It’s called Desert Varnish and it’s lovely. It may take 1000 years to form a layer as thick as one sheet of paper.

(B) Large area of fractured cliff wall, eight planes deep, about 15 yards wide

I’m intrigued again and again by the way sandstone fractures. This face is undercut in multiple layers; one can see a bit of the process of arch formation here (B). The visual texture is quite pleasing.

(C) Conchoidal fractures -- an especially beautiful example

Conchoidal fractures (C) happen when a slab of rock separates from the cliff wall. This example is particularly endearing, with its concentric circles. It was huge — scores of feet across.

And then, rounding a bend in the stream, THIS stares you in the face — an ancient pictograph (D). I am accustomed to seeing rock art in groupings, with multiple images on panels or nearby, but this one stands utterly alone. Sadly, it has been repeatedly used for target practice by rifle-bearing idiots; still, it commands my attention and respect.

(D) Lone pictograph high on wall; perhaps 16" diameter

1 Comment »

  1. Conchoidal fractures and pictographs – an intriguing place.

    Comment by chrisyoungman — April 20, 2010 @ 9:06 am | Reply

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