GEOLOGIC MAP OF THE TORREY QUADRANGLE, UTAH

The Torrey, Utah quadrangle is located in southern Utah, just west of Capitol Reef National Park and sits in the transition from the Basin and Range province to the Colorado Plateau. The quad exhibits spectacular exposures of relatively flat-lying Triassic, Jurassic, mid-Tertiary, and Quaternary units typical of the Colorado Plateau. Our map project builds on past mapping from the 1950s, and incorporates recent mapping data from nearby quadrangles and park areas produced in the last two decades. The Triassic deltaic-flood plain Moenkopi and fluvial-lacustrine Chinle Formations are exposed in most areas of the quad. The Jurassic eolian Wingate Sandstone is predominantly visible in the northern part of the quad. Jurassic units are principally exposed in the southern and northern parts of the quad and are mainly exposures of the fluvial Kayenta Formation, eolian Navajo Sandstone, and marine Carmel Formation, with few exposures of the Entrada Sandstone in the south. Intrusive igneous rocks of likely late-Tertiary age occur as basaltic dikes in the northern part of the quad.

The northern part of the quad has several NW-SE trending normal faults with <2 m offsets. The main structure in the area is the Teasdale Fault, which is a Laramide age NW-SE-trending feature with >200 m feet of offset . Our mapping helps constrain the location of the Teasdale fault and coincident monocline, which is exposed at the western edge of the quad, several outcrops in the valley, and at a long ridge of Navajo Sandstone known locally as the Cockscomb.

Quaternary cover occurs as colluvium and alluvium throughout the quad, and as debris flow deposits originating from Boulder and Thousand Lakes Mountain (e.g., the Teasdale bench on which the town of Teasdale sits). Many of these deposits were originally thought to be glacial in origin, but are now known to be debris flows. Debris flow deposits derived from both mountains are composed primarily of boulders of the Johnson Valley Reservoir andesite. Cosmogenic ³He dates on boulder surfaces give ages ranging from 10s to 100s of kyr; one debris deposit is currently active. The debris flow mapping provides a preliminary hazard assessment for the small towns of Torrey and Teasdale as well as the surrounding highway infrastructure.