Exploring where the geological fault lies

I stood in a long, shallow valley in a remote spot of Southern California. I could have been lulled into spending the entire day there, soaking up the springtime sun, enjoying the silence. I decided to text my family and share the bliss.

"Standing in the San Andreas Fault," I told them. "Eat your heart out."

I should have been thinking about the Big One, but mostly I was thrilled that I could get cellphone reception. If I had been thinking about the last big earthquake to strike this place, now known as the Carrizo Plain National Monument, I might not have had the courage to linger. In that 1857 quake -- the largest ever to strike the continental United States -- the earth jumped 30 feet.

I was in California with a group of geology enthusiasts from Minnesota, where our 10,000 lakes sometimes get in the way of seeing great rocks. We stocked up on gas and supplies, and caravanned to the plain, 100 miles northwest of Los Angeles. We were pulled by the San Andreas Fault. It slices across the Carrizo Plain, and nothing stands between you and the telltale signs of geologic power except, perhaps, the whimsical names assigned to those features.

We crisscrossed the fault by car and on foot. Right away, we noticed an occasional pond in the fault valley, something we hadn't expected to see. The area had just received torrential spring rains, but the ponds were there for another reason, as well.

All along the San Andreas, the Pacific and the North American plates grind past each other in a northwest-southeast direction. But things aren't that simple. Sometimes the plates pull away from each other, and the land between them often sags below the water table. That's when you get "sag" ponds.

We ventured off the main route, Soda Lake Road, and headed into the foothills of the Temblor Range, which parallels the fault on the east side of the plain. The dirt road with its boulders and washouts was a little hard on our vehicles (my companions' Toyota Corolla was definitely out of its league). People started to lose low-hanging car parts. It quickly became a trip ritual to stop and evaluate the mechanical necessity of lost or broken parts. Fortunately, we didn't lose anything essential.

Kinks in a stream

At the northern end of the monument we turned onto Elkhorn Road to see Wallace Creek, the geologic jewel of the Carrizo Plain. Scientists from around the world come here to study it, and many other streams, disrupted by the movement at the fault. Wallace Creek (dry when we were there) falls out of the Temblor Range until it reaches the San Andreas Fault, doglegs about 400 feet to the right, then straightens again and empties into the plain. The horizontal movement along the fault is so dramatic that the stream bed forms an unnatural kink, and rain is so scarce that the river lacks the erosional oomph to carve out a more direct route downhill.

Some of the older channels of the disrupted streams have been cut off completely from their upstream halves, beheaded, as they say.

Obsessed as we were by the fault, we didn't devote much time to the other attractions that draw visitors to the Carrizo Plain -- spectacular spring wildflowers, endangered species such as the San Joaquin kit fox, and internationally known Native American pictographs -- but those would be ample reasons to return.

Toward the end of the day, I stood in the fault valley again and waited for the earth to move. Good thing it didn't. Some parts of the San Andreas Fault creep steadily, but definitely not this part. A recent study of the Carrizo Plain showed that the fault ruptures (and that's the word geologists use) on average every 88 years. It's considered the most dangerous fault in Southern California, it skirts a sprawling metropolitan area with millions of people and it's overdue.

Andy Snyder, a geologist for the U.S. Geological Survey in Parkfield, Calif., sighed when I asked him this question. Maybe he gets it all the time. He reassured me that no, the fault doesn't form a fissure. "People don't fall into these faults and disappear." It isn't like the movies, he said.

And so close to Hollywood.