Signs of past California 'mega-quakes' show danger of the Big One on San Andreas fault

As Interstate 10 snakes through the mountains and toward the golf courses, housing tracts and resorts of the Coachella Valley, it crosses the dusty slopes of the San Gorgonio Pass.

The pass is best known for the spinning wind turbines that line it. But for geologists, the narrow desert canyon is something of a canary in the coal mine for what they expect will be a major earthquake coming from the San Andreas fault.
The pass sits at a key geological point, separating the low desert from the Inland Empire, and, beyond that, the Los Angeles Basin.
Through it runs an essential aqueduct that feeds Southern California water from the Colorado River as well as vital transportation links. It’s also the path for crucial power transmission lines.
California earthquake experts believe what happens at the San Gorgonio Pass during a major rupture of the San Andreas fault could have wide-ranging implications for the region and beyond.
They worry a huge quake could sever lifelines at the pass for weeks or months, cutting Southern California off from major highway and rail routes as well as sources of power, oil and gas. Southern California’s cities are surrounded by mountains, making access through narrow passes like the San Gorgonio essential.

The San Andreas fault, in heavy red, slices through key mountain passes including the San Gorgonio Pass and the Cajon Pass. (U.S. Geological Survey)

Experts have also expressed grave concerns about the Cajon Pass, where Interstate 15 and key electric and fuel lines run. Other problem spots are the Tejon Pass, through which Interstate 5 passes, and the Palmdale area, through which the California Aqueduct crosses.

http://www.latimes.com/local/lanow/la-me-ln-tour-san-andreas-fault-lucy-jones-20170613-htmlstory.html