Red Rock Pass

The sign's dates are radiocarbon years. Calibrated to the calendar, its 14,500 is about 17,500 years ago, which is why other sources give 18,000. The outlet was a dam of loose ground, an alluvial fan from Marsh Creek and landslide debris. When the lake topped it, the water cut down through it and the lake fell about 350 feet in a few weeks, to a sill of harder ground that became the level of the Provo shoreline. Water kept spilling through this pass for a long time after the flood, and the lake held at that level.

What the plaque says

Red Rock Pass You are standing in the outlet of ancient Lake Bonneville, a vast prehistoric inland sea, of which Salt Lake is a 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. 171 Text prepared by the Idaho Historical Society Marker made & installed by Idaho Transportation Department Text prepared by the Ida. Academy of Science & the Ida. Historical Society

Where it stands

Worth the stop nearby

• Boa Ogoi (Bear River Massacre Site) — 16 mi
  The Northwestern Band bought back the ground where its people were killed in 1863, and is turning farm fields back into the river bottom they knew.
• Lava Hot Springs — 18 mi
  The pools belong to the state because the springs left the Fort Hall Reservation and Congress handed them to Idaho in 1902.
• Preston and Napoleon Dynamite — 20 mi
  A farm town in the north end of Cache Valley that a former student turned into a set in the summer of 2003, without changing much of anything.
• Black Canyon of the Bear River — 22 mi
  A basalt gorge cut by a river that, most of the year, now runs past it in a pipe.

More markers nearby

• Utah & Northern Railway — 16 mi
• Bear River Massacre — 16 mi
• Range Wars — 17 mi
• Old Delta Sediments — 17 mi