OPEN-FILE REPORT 556
INTERIM GEOLOGIC MAP OF THE EPHRAIM 7.5-MINUTE QUADRANGLE, SANPETE COUNTY, UTAH
Hellmut H. Doelling, Paul A. Kuehne, and Douglas A. Sprinkel
The Ephraim quadrangle is located about 140 miles south-southeast of Salt Lake City in Sanpete County in central Utah. A diagonal line, extending NE-SW across the quadrangle, divides Sanpete Valley to the northwest, from the Wasatch Plateau. Sanpete Valley is a structural feature in which the San Pitch River flows south along its west margin. Quaternary fans form a gently sloping surface from the plateau front to the floodplain of the river.
Bedrock units are mostly of early Tertiary age. These include the (ascending) North Horn Formation (1100+ feet thick), Flagstaff Limestone (500–1000 feet thick), Colton Formation (1400+ feet thick), Green River Formation (620+ feet exposed), and the Crazy Hollow Formation (less than 50 feet exposed). Of these, the North Horn Formation may also have some Late Cretaceous strata at the base. The older three units are exposed in the Wasatch Plateau, the other two along the plateau-valley margin.
35 p., 1 pl., scale 1:24,000