Page "Big Bend National Park" Paragraph 12

Following the ending of rifting in the Late Cretaceous to the early Tertiary, the Big Bend area was subjected to the Laramide orogeny.

This period of ( now east-west ) compression caused the northeast-facing Mesa de Anguila ( an uplifted monocline on the southwest margin of the park ), the southwest-facing Sierra del Carmen – Santiago Mountains ( an uplifted and thrust-faulted monocline that forms the boundary of the park on the east ) and the Tornillo Basin.

During the middle Tertiary most of the volcanic rocks, including the Chisos group, the Pine Canyon caldera complex and the Burro Mesa Formation, formed.