Cristianitos Fault-San Diego County, CA

In case you think that hmm, San Onofre will be undercut, thankfully, solid concrete walls with a berm of large wedges of rocks buttress the plant and so time will be long coming before this nuclear plant is at risk.You can see the plant below and the layer of San Mateo Sandstone overlaid by the Alluvial Deposits (also, take care to see the nude sunbather, too ;-)

Next, let's look at the fault. It extends inland on a bearing of WNW for about 26 miles, crossing Ortega Highway, all the way through the valley of Cañada Chiquita. The Monterey Shale was laid down during the Miocene (20-15 million years ago) and the San Mateo Sandstone, during the Pliocene (4-5 million years ago. The Monterey Shale? Hey, where is that? Take a look below:

It's behind those bushes.

The San Mateo formation has moved over the Monterey Shale, which dropped allowing the situation to occur. Also, notice that banding has taken place near the fault in the San Mateo formation, while the Monterey Shale is crumpled and broken. But look at the layer of cobbles above the fault--they are level, which signifies no movement in the fault since they were laid down. The Alluvial Deposits are at roughly 90 degrees, which also means that they have not been displaced. Studies show that the wave-cut platform is about 120,000 to 125,000 years old; faults are considered active if they have moved within the last 11,000 to 35,000 years. Therefore, the fault is dead, and no worries over this one affecting San Onofre.

What's really neat, though, is that you can place your hand in a genuine fault. Way cool.

 

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