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Show 5 Lake Bonneville overflowed at least once and perhaps twice at Red Rock Pass at the northern end of Cache Valley, Idaho, into the Snake River drainage system. The overflow caused an exceptionally catastrophic flood with a flow of about 15 million cubic feet per second, which is four to five times the present average discharge of the Amazon River. Approximately 70,000 years ago, Lake Bonneville stood at the Bonneville Level for many years, then receded rapidly to a level even lower than that of the present Great Salt Lake. The Lake rose to the Provo Level about 25,000 years ago, receded again, then rose again to the Provo Level. During the past 12,000 years, it has receded to the present level of Great Salt Lake ( Durrant, 1952). The present Great Salt Lake has an elevation of roughly 4200 feet and is approximately 70 miles long and 40 miles wide. Its surface area is approximately 1500 square miles and its average depth is 13 feet, with a maximum depth of 35 feet. Total volume of the Lake when at an elevation of 4200 feet is 14.6 million acre- feet. The level and therefore the volume and density of the Lake still fluctuate widely, both annually and monthly. During the past century, the volume of the Lake has varied from a high of 32 million acre- feet in 1873, to a low of 10 million acre- feet in 1962, resulting in a brine density ranging from 14 percent to 29 percent. As the Lake receded toward its present elevation, many bars, beaches and deltas and several islands were formed. The largest of the islands are Antelope, Carrington, Fremont, Bird, Gunnison, Cub, and Dolphin. Although tradition had placed a large salt- water lake somewhere in western America long before 1776, the first authentic information |
