MAPPING AT THE EDGE OF GREAT SALT LAKE: GEOLOGIC MAPPING OF THE PLAIN CITY SOUTHWEST AND OGDEN BAY 7.5 MINUTE QUADRANGLES, NORTHERN UTAH

The Plain City Southwest (SW) and Ogden Bay 7.5’ quadrangles are in the northeastern part of Great Salt Lake in northern Utah, adjacent to the urban Wasatch Front. These two quads share a northern/southern boundary and contain the outlets of major mountain drainages, the Weber River (Ogden Bay), the Bear River (Plain City SW), and small subsidiary drainages. Our geologic mapping shows alluvial deposition has migrated over geologic and historic time due to fluctuating levels of Great Salt Lake. Little Mountain, a prominent bedrock knob ~450 feet of relief, has outcrops of Neoproterozoic Perry Canyon Formation, etched by shorelines of Holocene and Pleistocene lake cycles. Bedrock at Little Mountain exposes the westernmost part of a Neoproterozoic succession containing glacial deposits (diamictite), volcanic deposits (greenstone, pillow basalts), siltstones (slates), and a dolostone marker bed. These rocks were translated westward in the hanging wall of the Cretaceous Willard thrust, deforming in the process. This geologic map records important historical shorelines of Great Salt Lake. This terminal lake has experienced a significant contraction due to anthropogenic practices and climate change. Important developed wetland areas, including the Ogden Bay and Harold S. Crate State Waterfowl Management Areas, provide critical respite and habitat for native and migratory birds. Existing farming and evaporative mining operations as well as encroaching urban and industrial development make this map important for constraining geologic hazards and water resources. Our poster presentation highlights the geologic mapping of these two quadrangles as well as our cross sectional interpretation of the bedrock and the methodology used to complete the mapping using high resolution elevation data (lidar).