GEOLOGIC RECONNAISSANCE OF THE DALQUEST DESERT RESEARCH STATION, BIG BEND, TEXAS

The Dalquest Desert Research Station (DDRS) is a field locality owned and operated by Midwestern State University and located north of the Solitario uplift in the Trans-Pecos region of Texas (approximately bounded by 29.409944° - 29.55225° N and 103.811917° W – 103.766778° W). Its 3000 acres provides a diversity of geomorphic landforms modified by tributaries of the Alamo de Cesario Creek and other extant erosional forces. The canyon topgraphy produces exposures that elucidate the impact of Eocene and Oligocene volcanism and Basin and Range deformation. Volcanic and volcaniclastic materials dominate much of the stratigraphy, including rhyolite tuffs and basalt lavas. The property is cut by the E-W striking Tascotal Mesa fault as it intersects a complex NW-SE fault system.

We conducted a reconnaissance of the property as the first step to evaluating geologic problems on the DDRS and adjacent lands. We noted significant geologic variation among four areas we have informally named Purple Bench, Dry Falls, Breccia Springs and Arfvedsonite Hill. Purple Bench (29.568992° N, 103.773241° W) is a locality best known for its Uintan primate fossils. The area is marked by a locally purple-colored tuff that best correlates with the middle member of the Devil’s Graveyard formation. The soft tuff forms erosional pedestals capped with loose blocks of basalt. The Dry Falls (29.552514° N, 103.785828° W) is a pour off (arroyo knick point) along an Alamo de Cesario Creek tributary. It exhibits an extensive section of the conglomeritic basal unit of the Tascotal formation. including excellent exposures of thin lacustrine limestone beds. Breccia Springs (29.553852° N, 103.787325° W) sits on the Tascotal Mesa fault, juxtaposing the Tascotal formation with the Rawls Basalt. Proximal to the fault, the Tascotal exhibits a number of deformation features, including folding and additional faulting. The Rawls layers are tilted but not folded; the base contains a distinctive breccia layer comprised of angular basalt clasts in a calcite matrix. Arfvedsonite Hill (29.556582° N, 103.797774° W) is the northernmost of three hills underlain by the blue-colored Terneros Creek Rhyolite, an intrusive rock with small sodic amphiboles in a matrix of microfelsite. Much of the hill's surface is covered by intensely fractured and red-stained buff colored rock.