|Red Rock Pass was cut
through a sill of resistant Paleozoic shale, limestone, and dolomite, and
forms a narrow gap two miles long. At one time the pass was at the shoreline
of Pleistocene Lake Bonneville, 300 feet higher. Lava flows in the vicinity
of Pocatello diverted the Bear River through Lake Thatcher into Lake
Bonneville. The sudden influx caused Bonneville to overflow at Red Rock.
Marsh Creek Valley, immediately downstream, was flooded from wall to wall,
and the rapid discharge eroded the pass to its present level. The Bonneville
Flood, as it is known, was catastrophic. Maximum discharge as about 15
million cfs, or about three times the average
flow of the Amazon, the world's largest
rate of flow was approximately sixteen-mph,
and though peak flow lasted only a few days,
voluminous discharges may have continued for
at least a year.
Red Rock pass attracts geological groups from miles
around, to study the remains of the great forces on nature.
Darrel La Mar
Wakley) (Right -Artist L.A. Ramsey's interpretation of Lake Bonneville
flooding through Red Rock Pass.)