NEW GEOLOGIC MAP OF THE BOUNTIFUL PEAK 7.5' QUADRANGLE IN NORTHERN UTAH, USA: A GEOLOGIC STORY OF UNCONFORMITIES AND GEOLOGIC HAZARDS

New mapping provides the first detailed geologic map (1:24,000 scale) of the Bountiful Peak 7.5' quadrangle, Davis and Morgan Counties, Utah. The quadrangle is located northeast of Salt Lake City. Parts of the cities of Bountiful, Centerville, and Farmington occupy the west part of the quadrangle. The central and east parts of the quadrangle are dominated by rural, rugged, and steep mountainous terrain of the northern Wasatch Range. The bedrock geology in the quadrangle includes Paleoproterozoic metamorphic rocks of the Farmington Canyon Complex that are overlain by Cambrian, Cretaceous, and Paleogene sedimentary rocks. Major unconformities separate each age group of bedrock units. These rocks record a complex history of tectonic events including: 1) Paleoproterozoic sedimentation, volcanism, plutonism, and metamorphism, 2) carbonate and siliciclastic deposition along a slowly subsiding continental passive margin, 3) contractional deformation during the Sevier orogeny, 4) orogenic collapse following the Sevier orogeny, and 5) extensional deformation related to modern Basin and Range extension. The metamorphic rocks are commonly deeply weathered and altered to clay minerals. Clay-rich minerology and steep terrain has resulted in numerous landslides throughout the quadrangle. The urbanized valley part of the quadrangle contains the southern part of the Weber segment of the active Wasatch fault zone, a major segmented normal fault zone that bounds the east side of the Basin and Range and creates the stark topographic rise of the Wasatch Range. This active fault zone presents a significant earthquake hazard to the communities along the fault.

Previous geologic mapping in the area was done at 1:50,000 scale in the 1970s. New mapping utilized multiple tools to improve precision and accuracy of the map. New high-resolution lidar enhanced identification of landslides, debris flows, fault scarps, and bedrock contacts that are otherwise obscured by dense vegetation. Historical aerial photographs from the 1950s and 1970s, geotechnical reports, and water well data enhanced the mapping of surficial deposits and fault scarps now obscured by urban development. The use of Esri’s Collector application enabled digital acquisition of georeferenced field notes and photos, which streamlined map compilation efforts.