Interim Geologic Map of the Plain City Southwest 7.5' Quadrangle, Weber and Box Elder Counties, Utah

The Plain City Southwest (SW) and Ogden Bay 7.5′ quadrangles are in Weber, Box Elder, and Davis Counties. The quadrangles include parts of the communities of Hooper, Warren, and Reese, the Harold Crane Waterfowl Management Area, several waterfowl wetlands, as well as the southwestern corner of Willard Bay Reservoir. The North Fork and South Fork of the Weber River f low south into the Ogden Bay Wildlife Management Area at the edge of Great Salt Lake. The northwestern part of the Ogden Bay quadrangle and the southwestern part of the Plain City SW quadrangle contain most of Little Mountain, a small bedrock mountain with about 500 feet of relief. The western side of Little Mountain as well as the northern part of the Plain City SW quadrangle are part of Willard Bay of Great Salt Lake. Small meandering channels flow into the bays from local drainages. Numerous evaporation ponds related to industrial minerals production cover the central western and northwestern part of the Plain City SW quadrangle, obscuring geologic deposits. This mapping project will provide the basis for identifying and delimiting potential geologic hazards in future Utah Geological Survey (UGS) geologic hazard maps, part of the UGS Geologic Hazards Mapping Initiative (Castleton and McKean, 2012). Mapping for the project was done on stereographic pairs of aerial photographs from the following sources: black-and-white aerial photographs from the U.S. Department of Agriculture (USDA) Agricultural Stabilization and Conservation Service (1958, 1965, 1971a, 1971b). Mosaics of some USDA photographs were accessed using the Weber County web services (USDA Agricultural Stabilization and Conservation Service, 1937, 1962, 1980, 1985). Additional aerial photography sets from the National Agricultural Imaging Program (NAIP) were used (Utah Geospatial Resource Center [UGRC], mid-1990s, 2006, 2009, 2011, 2016a, 2018a, 2021a) as well as high-resolution (15cm) Hexagon imagery (Utah Geospatial Resource Center, 2021b). Most Quaternary unit contacts, including human disturbed areas, were mapped using two lidar elevation datasets (Utah Geospatial Resource Center [UGRC], 2016b, 2018b). The geologic map was made by transferring the geology from the aerial photographs to a geographic information system (GIS) database using the programs ESRI ArcPro and Global Mapper v. 18 for a target scale of 1:24,000. Cross section A-A′ was created in Adobe Illustrator. Field-based investigations included shallow subsurface investigations in targeted areas with a soil auger. Materials from 1 to 3 meters were observed, documented, and sampled, which aided in preparing descriptions of most Quaternary units.