This full-color, oversize map, designed for hikers in the park, describes geologic units and features. The text documents the geologic history of the Big Bend Ranch State Park area. Support was provided by the Texas Parks and Wildlife Department and the U.S. Geological Survey.

The Bofecillos Mountains and Big Bend Ranch State Park contain a complex sequence of volcanic, volcaniclastic, and intrusive rocks that erupted from sources both within and outside the area.

The Solitario is a circular, 14- to 16-krn-diameter, mid-Tertiary laccolithic dome and caldera in southern Trans-Pecos Texas; it is among the world's largest laccoliths.

The 37-Ma-old Infiernito caldera of the northern Chinati Mountains is a major eruptive center of the mid-Tertiary volcanic field of Trans-Pecos Texas. Volcanism in the Chinati Mountains began with eruption of a sequence of rhyolitic to trachytic lavas, the precollapse lavas.

Cretaceous sedimentary rocks and Tertiary intrusive, extrusive, and volcaniclastic rocks dominate the geology of the Hen Egg Mountain and Christmas Mountains quadrangles in the Big Bend region of Texas.

Geologic map that depicts the surface geology of Hardeman, Wilbarger, Wichita, Clay, Knox, Baylor, Archer, Haskell, Throckmorton, Young, and Foard Counties and part of Jack County, Texas. The 20-page booklet indicates geologic formations, abbreviations, and ages.

This compilation of potassium-argon (K-Ar) ages of igneous rocks of the Tertiary volcanic field of Trans-Pecos Texas includes all published ages known to us as well as many unpublished results.

The Van Horn Mountains caldera is a small (~10-km2) igneous center in the Trans-Pecos volcanic province. The caldera formed 37 to 38 mya during eruption of the first of two ash-flow tuffs related to the caldera.