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