One of the most dramatic sections of road in the Big Bend is between Alpine and Marfa in which the highway cuts through the Paisano Volcano and the three-mile diameter Paisano Caldera. The caldera is mapped as chaotic terrain and has sunk about 1,000 feet in its northwest corner and less elsewhere. Volcanoes are terrifyingly violent when erupting and the photograph above shows a fossil mudflow, a lahar as they are known in Indonesia, full of pebbles and rock fragments.
The photograph below, taken from the same road cut 9.7 miles west of Alpine shows a block of red Morrow tuff in a tuffaceous mudstone matrix. For more on the caldera see Davis Mountains Vistas.