Red_Rock_Pass
Red Rock Pass (Idaho)
Mountain pass in Idaho, United States
Red Rock Pass is a low mountain pass in the western United States in southeastern Idaho, located in southern Bannock County, south of Downey. It is geologically significant as the spillway of ancient Lake Bonneville. It is traversed by U.S. Route 91 at an elevation of 4,785 feet (1,458 m) above sea level,[1] bounded by two mountain ranges; the Portneuf to the east and the Bannock to the west.
The pass was cut through resistant Paleozoic shale, limestone, and dolomite, and forms a narrow gap two miles (3 km) in length.[2] At one time the pass was 300 feet (90 m) higher, where the shoreline of Pleistocene Lake Bonneville stood.
The pass takes its name from the red limestone cliffs which border it.[3] Red Rock Pass has a surface deposit of calcareous silty alluvium with topsoil of dark grayish brown silt loam.[4]