Paisano Pass Volcano Collapse Breccia

If you’ve ever gone to see the mysterious Marfa Lights in far west Texas, chances are you’ve driven right through the caldera of the massive Paisano volcano (yes, there are volcanoes, although extinct, in Texas). This particular one left a crater three miles in diameter.

These pictures show a sort of cross-section of that collapse on a roadcut on Hwy 90 between Alpine and Marfa. This area would have been inside the volcano when it was active, but once the magma chamber finally emptied itself, it could no longer support the weight of the earth above. Boulders and geologic debris fell as the volcano caved in on itself; these rocks and boulders were then re-cemented to create the "collapse breccia" you can see in the images above.

References:
Speaking of Geoscience GSA Guest Blog, "Big Bend Snapshot of History Project's Geology of the Paisano Pass Volcano", https://speakingofgeoscience.org/2012/04/12/big-bend-snapshot-of-history-projects-geology-of-the-paisano-pass-volcano/​