This is the cover photograph of Big Bend Vistas. The photograph is of The Window, taken from Ross Maxwell Scenic Drive at 5:40 p.m. Vernon Bailey Peak is at left, then The Window, next the sharp Carter Peak, and Ward Mountain on the right, all mountains carved from the granitic Chiso Mountains Pluton (a pluton is a large igneous intrusion). The dome of the extinct volcano Casa Grande is on the skyline through The Window.
As I say in the book in a caption to a photograph of The Window from the Basin: “many visitors wonder if the Chisos Basin is a volcanic crater. However, it is just the result of erosion. The Window developed along jointing in the Chisos Mountains pluton, jointing parallel to mineral lineation in the intrusion. Mineral lineation occurs when platy minerals line up in a common orientation, perhaps from pressure, and result in weakened zones in the rock.”
The Chisos Mountains pluton, as it ascended, brought up Cretaceous Pen and Boquillas strata with it and perhaps some Chisos tuffs. South Rim strata, if they extended over the Basin, would have been broken up. The soft Cretaceous beds eroded through The Window as it deepened.
The Basin is now about 2,000 feet below the general level of the surrounding mountaintops, and is still eroding down. Erosion is creating a similar gap at Panther Pass, already 1,000 to 1,500 feet below the tops on either side.
Click on the photograph to bring up a larger image.
