Geology
The foundation of the reservoir is a steep-sided narrow canyon composed of siliceous sandstone and hard quartzites inter-bedded with softer shales, siltstones, and argillites. About 1.5 miles (2.4 km) east of the dam, a road cut has revealed a fault scarp on the southbound side with about 9 feet (3 m) of slippage.
Read more about this topic: Flaming Gorge Reservoir