Red Rock Pass is a mountain pass in Idaho that is famous for being the spot at which the ancient Lake Bonneville was emptied.

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.

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, the valley immediately downstream of the pass was flooded from wall to wall, and the rapid discharge of water eroded the pass to its present level.

The flood followed the path of the Snake River Plain, generally following the path of the present-day Snake River.

The Bonneville Flood, as it is known, was a catastrophic event. Maximum discharge as 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.