Geologic Map of the St. George 7.5' Quadrangle, Washington County, Utah (GIS Reproduction of UGS Map 251DM [2011]) (M-291dr)

By:  Janice M. Hayden and Grant C. Willis

In 2021, through U.S. Geological Survey cooperative agreement G20AC00389 (2020) funding, the UGS compiled geologic map 251DM (2011), into a new GIS database and Geologic Map Schema (GeMS). During this project, the UGS made minor changes to the geologic map based on recent geologic studies in the area. See Errata Sheet at the back of the text booklet for a detailed list of changes.

The St. George 7.5’ quadrangle extends from the Red Hills north of St. George city south across the rugged Bloomington dome to the hummocky White Hills at the south edge of the quadrangle. Colorful red, orange, white, and gray strata from the Permian Kaibab Formation to the Jurassic Navajo Sandstone have been compressed into the broad, poorly defined, northeast-trending St. George syncline and the much tighter Virgin anticline. The potentially active Washington and St. George faults offset strata 400 to 750 feet. Other small faults near folds generally developed in pairs, forming grabens. Four Quaternary basalt flows, which followed stream drainages from vents north of the quadrangle, now form black ridges (inverted valleys) that frame the brightly colored sedimentary rock. Recent incision by the Virgin and Santa Clara Rivers and their tributaries exposed the multi-colored strata and created several major gravel terraces.