GEOLOGIC MAP OF THE NORTHEASTERN DAVIS MOUNTAINS, TRANS-PECOS TEXAS

A new geologic map, compiled mostly from mapping in the 1980’s, shows geologic units and features over an area stretching from Gomez Peak in the north to Star Mountain in the south, and from Adobe Canyon in the west to the Barilla Mountains in the east. Relief in the area ranges from about 3500 feet in low valleys on the northeast to about 6500 feet in the southwest. The front of the Davis Mountains is structurally controlled by northwest-trending basin-and-range faulting, expressed partially as drape folds over deep-seated faults in late Paleozoic evaporite units. These structures form the northeast margin of a large structural depression containing the Davis Mountains volcanic field.

Volcanic strata (~39 to 36 Ma) with a total thickness of approximately 800 meters (~2,500 feet) overlie lower to upper Cretaceous strata. Basal volcaniclastic Huelster Formation, locally containing mafic to silicic lava, is overlain in the north by the Gomez Tuff ignimbrite and in the southeast by Star Mountain Rhyolite silicic lava. The Gomez Tuff (up to 500 m thick) was erupted from the Buckhorn Caldera, which lies south of the type locality of Gomez Peak. Within the caldera, the Gomez is overlain by coarsely-porphyritic lava of the Buckhorn Trachyte. Elsewhere along the Davis Mountains front, the Gomez is overlain by Adobe Canyon Rhyolite lava, which locally overlies Buckhorn Trachyte. This local section is overlain by Tricky Gap Rhyolite lava, Barrel Springs Group ignimbrites and other units, mostly derived from vents to the southwest of the mapped area. Large quartz trachytic sill to laccolithic intrusions were emplaced along the Cretaceous/Tertiary boundary. A few younger undated basin-and-range basaltic intrusions are located near faults along the mountain front.

Although the area is dominated by alkaline silicic lava and tuff, mafic to intermediate lava, although volumetrically minor, is present at every stratigraphic level.