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.

This report describes preliminary results of an ongoing study of the volcanic stratigraphy, caldera activity, and known and potential mineralization of the Chinati Mountains area of Trans-Pecos Texas. Many ore deposits are spatially associated with calderas and other volcanic centers.

Lignite development will place major demands on ground-water supplies.