Cajon Pass: The Choke Point Between Two Worlds

The pass you are climbing is the gap between the San Gabriel and San Bernardino Mountains, and it has been a corridor for ten thousand years because there was no other way through. The Serrano and Cahuilla peoples used this pass as a trading route between the Mojave Desert and the coastal valleys long before any road existed. The Spanish called it Puerto de San Carlos.

The Old Spanish Trail, which connected Santa Fe to Los Angeles, came through here in the eighteen thirties. The Mormon Road, bringing Brigham Young's missionaries south from Salt Lake, came through here in the eighteen fifties. The railroad came in eighteen eighty-five.

The highway came after that. The pass is now occupied by two freight rail lines, the BNSF and the Union Pacific, and Interstate Fifteen, all of them threading through the same narrow canyon because there is no alternative. On a busy freight day, over one hundred trains pass through Cajon Pass.

The combined train and truck traffic through this gap represents a significant fraction of all goods moved between the Pacific ports and the interior of the continent. The logistics are impressive. The geology is more impressive.

The San Andreas Fault runs through the floor of this canyon. You are driving across an active tectonic boundary. The ground here moves, has moved, and will move again, the same fault system responsible for every major earthquake in Southern California history.

When you smell the creosote and feel the grade flattening at the top of the pass, you have crossed from the coastal drainage to the Mojave. The light changes. The air dries.

The vegetation shifts. You are in a different place.