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The low ridge at the south end of This valley forms the south rim of the Great Basin, which in prehistoric times was the bed of a vast body of water now referred to as Lake Bonneville.

Lake Bonneville extended 350 miles to the north and was in places 145 miles wide with a maximum depth of 1050 ft. It’s shorline is clearly disernible on the mountain slopesfringing the basin through Red Rock Pass in what is now southern Idaho, the lake drained to the Pacific Ocean, it’s waters flowing down the Prtneuf, Snake, and Columbus rivers.