Below is a typical view as you make your way down the creek that forms Boot Canyon. This is a classic V-shaped, water-carved valley, as opposed to a U-shaped glacially formed valley. (Of course, you wouldn't expect glacier activity in the recent geological history of Texas.)

The erosion proceeds by two basic methods. In the stream bed itself (when it rains) flood waters carry abrasive material - mostly silt and sand - that eats into the underlying volcanic rock like sandpaper. This produces the polished bedrock effect seen in the next image. The sides of the valley are exposed to chemical weathering and "creep". Creep is the process where gravity gradually pulls the loosened rock and soil down toward the stream bed. (As a geologist in the field, this is the only kind of creep you hope you'll come across.) Once it is within reach of the flood waters, it is entrained in the flow. By these two processes the canyon is deepened and widened.

The image below is a picture of the famous "Cowboy Boot" from which Boot Canyon obviously gets its name. The "boot" was formed by erosion along fractures (called joints in geological terminology) in the Wasp Spring Flow Breccia. Enjoy it while you can, because, like the recently deceased "Old Man of the Mountain" in New Hampshire, it will inevitably succumb to the erosion that gave it form. My brother, very sacrilegiously, would like to rename this feature "The Can-Can Dancer". We may have to excommunicate him from the fellowship of Texans.

I was a bit dismayed to see some rock climbers had recently scaled the Boot and left cables and whatnot on it. If you do rock climbing in Big Bend you need a permit, AND you need to pack out all your stuff. Note Crown Mountain in the background. It is composed of the Lost Mine Rhyolite and the Wasp Spring Flow Breccia (now apparently collectively called, as explained in the piece on the South Rim Trail, the Boot Rock Formation).

This last view is from Boot Canyon, across Tornillo Creek, and toward the Sierra del Carmen. The Brown Rhyolite should probably be now designated as the Pine Canyon Rhyolite. (For further explanation, go to the link below for the South Rim Trail.) The Pine Canyon Rhyolite lies unconformably on top of the Chisos Group (formerly, Chisos Formation). "Unconformably" means there was an extended period of time when nothing was deposited and probably a lot was eroded away. Since such unconformities indicate missing rock units, they are gaps in the geological record. All they "record" is that there was a certain length of time (several millions of years in this case) when non-deposition and erosion reigned.

FORWARD to Boquillas Canyon

BACKWARD to the South Rim Trail

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