NEW GEOLOGIC MAPPING OF THE BOUNTIFUL PEAK 7.5' QUADRANGLE, DAVIS AND MORGAN COUNTIES, UTAH

Recently completed geologic mapping of the Bountiful Peak 7.5' quadrangle (UGS OFR-703DM, fieldwork done 2017–18) has resulted in the first complete geologic map of the quadrangle at 1:24,000 scale. The quadrangle is in southern Davis and Morgan Counties, just northeast of Salt Lake City, Utah. Parts of the cities of Bountiful, Centerville, and Farmington occupy the western part of the quadrangle in the valley and foothill areas. The central and eastern parts of the quadrangle are dominated by rural, rugged, and steep mountainous terrain of the northern Wasatch Range and Sessions Mountains.

The bedrock geology in the quadrangle is dominated by Paleoproterozoic metamorphic rocks of the Farmington Canyon Complex (FCC), which has a complex history with peak metamorphism reaching amphibolite facies around 1700 Ma, followed by overprinting retrograde metamorphism related to deformation during the Cretaceous–Paleocene Sevier orogeny. Mapping of the FCC is primarily based on work by Bryant (1988, 1:50,000 scale) but includes improved locations of some contacts. Cambrian strata are exposed on the east side of the quadrangle and this map shows the Cambrian Bloomington, Nounan, and St. Charles Formations, which were previously not recognized in this area. The Proterozoic and Cambrian rocks are unconformably overlain by Cenozoic clastic rocks that record extensional orogenic collapse and basin-and-range extension. This map documents a unique cobble- to boulder-gravel deposit that is present on the crest of the Wasatch Range and is here interpreted as a Miocene deposit but was previously mapped as part of the Paleocene to Eocene Wasatch Formation.

Geologic hazards in the quadrangle include, but are not limited to, landslides, floods, debris-flows, and the seismically active Weber segment of the Wasatch fault zone (WFZ). Half-meter lidar data and stereographic photographs from 1958 were used to improve accuracy and precision of mapping of surficial deposits and previously unrecognized strands of the WFZ. Deposits and shorelines of Pleistocene Lake Bonneville are prominent within the quadrangle at and below about 5200 feet elevation and are commonly cut by the WFZ. This map documents over 300 previously unrecognized mass-movement deposits.