Wednesday, November 18, 2015

A Guide to Earthquake Tourism Along the San Andreas Fault

Photo: Sandi Hemmerlein

by Sandi Hemmerlein

The San Andreas Fault, the boundary between the Pacific and North American tectonic plates, caused California's worst disaster in recorded history: the 1906 San Francisco earthquake. To this day, scientists are still learning about numerous other seismic events that happened through the ages.

If you'd like to get to know this mischief-maker known as San Andreas before it makes itself known as the "Big One," you won't have to go very far. More than 700 miles of it stretch from Northern California to the Salton Sea. There are plenty of places in its southern segment known as the Mojave section, where you can see signs of the movement of the two plates on either side -- the Pacific plate to the west, and the North American plate to the east.

However, to chase down our faulty friend, you have to look closely -- and you have to know what to look for. The San Andreas Fault is more than a mile wide in some locations, and its signs may be as subtle as a dip in the road, a bend in railroad tracks, or a change in direction in a creek or a stream. Most of the places that you can visit along the San Andreas Fault show signs like these of the crustal bending and fault slipping, but there are places where you can actually see -- and touch! -- the fault itself.

Channel Islands National Park: To go back to where it all started, take a look at the Channel Islands. The Pacific Plate's tectonic movement that brought it to meet the North American Plate directly caused their formation in the Pacific Ocean. Their current orientation and elevation are a result of tectonic plate movement over the last five million years, but the plates haven't actually stopped. Since being formed, the islands have rotated clockwise about 100 degrees, and continue to turn and rise.

Although signs of San Andreas are usually more visible from a bird's eye view, you can get a great visual of the islands' geologic uplift from the deck of a boat. Island Packers is a company that frequently runs ferries from Ventura and Oxnard to the islands for day trips, camping overnights, and sea cruises. Channel Islands Kayak Center also conducts kayak tours of the sea caves of Anacapa and Santa Cruz Islands.

Carrizo Plain National Monument: One of the most important geological sites in the world is one of Southern California's best-kept secrets: Carrizo Plain National Monument. Located 65 miles west of Bakersfield, Carrizo Plain features an alkaline lake that remains dry most of the year, but when wet, it's fed by Wallace Creek, a small stream that also happens to be a world-famous section of the fault. If you climb up atop a ridge along the Wallace Creek Interpretive Trail, you can see a very well defined surface expression of the fault trace -- basically, the plate boundary, in plain view. And because it's so arid there, the fault hasn't suffered any significant erosion.

The signs of it are also relatively recent. In the 1857 Fort Tejon earthquake (magnitude 7.9), the fault moved 30 feet at Wallace Creek, making the stream channel look crooked, as it does today. And, like the Channel Islands, it's still moving -- as much as 1.3 inches a year. Here, you can get both incredible first-hand accounts and views of plate tectonics in action.

Antelope Valley: There are several sites in and around Palmdale where the San Andreas Fault is accessible. Just north of Avenue S, CalTrans bisected the San Andreas Fault to make way for Highway 14. Folded layers of rock strata, which have been contorted by compressional forces, were henceforth exposed. About 25 miles southeast of the roadcut, investigators also cut the fault at Pallett Creek, creating a trench along the banks of the creek where radiocarbon dating earned it the nickname "the Rosetta Stone of Paleoseismology." You can walk right up to the trench and analyze the layers of rock, like counting rings on a tree stump. You can even put your hands on it or lean against it -- and wait for the earth to move.

Another five miles east, conspicuous signs of the San Andreas Fault are visible at Devil's Punchbowl Natural Area, which lies within the fault zone and has its own fault called the Punchbowl Fault. Here, you can also see how intense pressures created dramatic folding of rock, and how ongoing uplift action caused steeply tiled geologic formations. Explore this county park on your own, or join one of the Punchbowl naturalists on a San Andreas Fault tour, conducted every Sunday at 1 p.m.

San Gabriel Mountains: The San Andreas Fault not only forms the northern boundary of the San Gabriel Mountains, but it also formed the mountains themselves. To see evidence of it, visit the Big Pines Ranger Station, which actually sits on top of the fault trace. Drive along Big Pines Highway, and along the side of the road you'll see piles of exposed rock that have been ground into dust by seismic activity over the ages (a "fault gouge").

You have San Andreas to thank for some of the recreational areas in the San Gabriels, including the fault-bounded Jackson Lake in Angeles National Forest and Lost Lake in San Bernardino National Forest. Both were created by the fault, and both run along the fault line. Lost Lake, a body of water formed in a sunken patch of land between two fault strands, is particularly intriguing as no streams empty into it. The water just comes up out of the fault, fed by deep natural springs. Legend has it that this sag pond is a "bottomless lake" -- and gets its water from the center of the earth. Fishermen still try to throw a line in there to see what they can catch, even though the lake hasn't been populated with fish in decades. But there's plenty of other wildlife to view and enjoy, including some endangered birds like Bell's vireo, the southwestern willow flycatcher.

Inland Empire: After the San Andreas Fault works its way through the eastern San Gabriels along the Cajon Pass, it then traverses the southern boundary of the mountains as it moves farther east. In Highland, just outside of San Bernardino, you can observe the fault's handiwork at Plunge Creek, offset by more than 300 meters over time. Several trenches were dug here along the fault, and radiocarbon dating indicates that an earthquake offset the creek sometime between the 15th and 18th centuries. If you'd rather take a look at the San Andreas Fault without the danger of it lurking directly underfoot, visit the Hall of Geologic Wonders at the San Bernardino County Museum in Redlands, which houses actual peels from the Pallett Creek portion of the San Andreas Fault.

In the Coachella Valley, you can take your earthquake tourism to a whole new level with a jeep tour with Desert Adventures or Covered Wagon Tours. If it's not too hot out, hoof it and explore the fault on foot at Mission Creek Preserve and Thousand Palms Oasis, both of which are along the fault line. Enjoy the hot mineral springs any season, day or night, at Two Bunch Palms in Desert Hot Springs, whose healing waters are reportedly released from deep beneath the earth's surface by geological activity related to San Andreas.

The Salton Sea: The Salton Sea usually attracts a certain kind of visitor -- "snow birds" who come for the winter, photographers building their portfolios, and birdwatchers hoping to catch a migration or two. But for earthquake tourists, there are plenty of signs of the San Andreas Fault here, running along the North Shore and down to Bombay Beach and the State Recreation Area to the east of the sea, where it terminates. There is a high potential for seismic activity the Brawley Seismic Zone -- especially with the nearby Imperial Fault -- but the most fascinating thing to see here is the effect of the San Andreas Fault within the Salton Sea Geothermal Field.

Near the Sonny Bono National Wildlife Refuge at the southern tip of the sea, you can find the "boiling mud pots," where high heat emanates from zones of partially molten rock deep below the Earth's surface, causing first violent, and then tiny, eruptions. Over time, this active volcanic activity -- the only active volcanoes in Southern California -- create lava domes, officially known as The Salton Buttes. Earthquake swarms are common and persistent here, making your chances for experiencing seismic activity while you're touring the San Andreas Fault very high. Just be careful of the sulfuric steam being spewed out of the mud pots as you explore. And watch where you step across the fragile and cracked landscape.
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