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Program Manager: Grant C. Willis (UGS) Project Manager: Robert F. Biek (UGS) GIS and Cartography: Lori J. Steadman, Jay C. Hill, Kent D. Brown, J. Buck Ehler (UGS) Geology review: Grant C. Willis, Robert F. Biek, Michael D. Hylland (UGS)
GIS review: Kent D. Brown (UGS) Funding: Utah Geological Survey and the U.S. Geological Survey, National Cooperative Geologic Mapping Program, through USGS STATEMAP award number 1434-94-A-1256 (1994). Updated and converted into national Geologic Map Schema (GeMS) using funding through U.S. Geological Survey National Geologic Map Database Agreement G20AC00389 (2020). |
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This digital dataset represents the geology of the St. George 7.5' quadrangle at 1:24,000 scale. Strata in the quadrangle have been compressed into the broad, north northeast-trending, poorly defined St. George syncline and the much tighter Virgin anticline. Bloomington dome, the southern-most of three domes in the Virgin anticline, is in the center of the quadrangle. The Permian Kaibab Formation crops out in the center of Bloomington dome as the oldest unit in the quadrangle. The Triassic Moenkopi Formation, which unconformably overlies canyons and ridges eroded into the Kaibab Formation, is attenuated over Bloomington dome. The Triassic Chinle Formation is also exposed on both limbs of the anticline. The Jurassic-Triassic Moenave Formation, and Jurassic Kayenta and basal Navajo Sandstone, are exposed only on the north limb of the anticline within the quadrangle. Four Quaternary basalt flows followed stream drainages from vents north of the quadrangle. Because of continued regional uplift and subsequent erosion of adjacent sedimentary rocks, these flows now cap ridges, forming inverted valleys. Uplift and downcutting are also documented by incised alluvial-terrace deposits with thick calcic soil along the Virgin and Santa Clara Rivers and their tributaries. Only two faults, both trending northward, have more than a few tens of feet of offset. The Washington fault offsets strata about 750 feet (230 m) where it crosses the northeast corner of the quadrangle. The St. George fault offsets strata about 400 feet (120 m) and cuts across the north-central part of the quadrangle. Both of these are considered late Cenozoic and potentially active extensional faults, but neither offsets exposed surficial deposits in the quadrangle. Most other faults trend north-northwest, roughly perpendicular to the Virgin anticline. These small faults generally developed in pairs, forming grabens, and may be related to formation of the folds or to basin-and-range faulting. This item is part of a larger digital dataset that contains the feature classes, base maps, plates, and other supplementary materials necessary for the user to fully view, evaluate, and utilize the geological spatial data related to this product. A paper version of this map is available from the Natural Resources Map & Bookstore. |