You are standing in the outlet of ancient Lake Bonneville, a vast prehistoric inland sea, of which Salt Lake is modern remnant
Covering over 20,000 square miles when it overflowed here about 14,500 years ago, its winding shoreline would have stretched from here to New Orleans if it were straightened out. This pass was deepened considerably when Lake Bonneville began to flow into Snake River. For a time, a torrent several times larger than the Amazon was discharged here. Finally, with a hotter drier climate that slowly emerged about 8,000 years ago, Lake Bonneville gradually disappeared.