Red Rock Pass
From Wikipedia, the free encyclopedia
| Red Rock Pass | |
|---|---|
 Red Rock Pass |
|
| Elevation | |
| Location | Idaho,  United States |
| Range | Portneuf Range/Bannock Range |
Red Rock Pass is a mountain pass south of modern day Downey, Idaho that is famous for being the spot at which the ancient Lake Bonneville was emptied. It is bounded by two mountain ranges; the Portneuf to the East and the Bannock to the West.
The pass was cut through a sill of resistant Paleozoic shale, limestone, and dolomite, and forms a narrow gap two miles (3 km) long. At one time the pass was 300 feet (100 m) higher, where the shoreline of Pleistocene Lake Bonneville stood.
[edit] The Bonneville flood
It is believed that lava flows in the vicinity of Pocatello, Idaho, began to divert the Bear River through Lake Thatcher and then into Lake Bonneville. This sudden influx caused Bonneville to overflow at Red Rock. This overflow caused a sudden erosion of unconsolidated material on the northern shoreline near Red Rock Pass. As the material gave way, Marsh Creek Valley, immediately downstream, was flooded from wall to wall, and the rapid discharge eroded the pass to its present level. The flood then flowed into the Snake River Plain, generally following the path of the present-day Snake River to its outlet in the Pacific Northwest.
The Bonneville Flood, as it is known, was a catastrophic event. The maximum discharge was about 15 million cubic feet per second (420,000 m³/s), or about three times the average flow of the Amazon River, the world's largest river. The speed of flow was approximately 16 mph (7 m/s), and though peak flow lasted only a few days, voluminous discharges may have continued for at least a year.
