Cruisin' Down the Fault Line

john's picture

The San Andreas fault is visible from space.  A long scar on the earth, the fault winds its way south from Mendocino, Fort Ross and San Francisco, through central California to Tejon Pass, then north of Los Angeles to Cajon Pass and San Bernadino, finally leaving the state by way of the Imperial Valley to Mexico and the Gulf of California.

Many years ago, we left a scientific conference to drive south along the fault line to see the geological features for which the fault is justly famous.  Geologists love this trip.  It was a spectacular late autumn day in northern California.  The scent of hay, vines and falling leaves lay in the air. 

Our first stop was Crystal Springs Lake.  Near the south end of the lake, where highway 92 crosses the reservoir, you can still see an offset sandbar where the 1906 earthquake displaced the land.  There we reflected on the great 1906 earthquake and fire, in which thousands of San Francisco residents died.  After the destruction, army engineers bulldozed much of the debris into the bay, creating land upon which later structures were built.  In a strange echo of 1906, several of those structures in the Marina district were destroyed again by the 1989 Loma Prieta earthquake.  The soft landfill from 1906 was transformed to a liquefaction state by the violent shaking from seismic waves propagating north from the Loma Prieta epicenter. 

Following highway 280 south to California 101, we drove south through Morgan Hill, Gilroy and Steinbeck country until we came to Hollister.  Here the fault shows a type of slow, non-seismic slip, displacing the two sides of the fault at the steady rate of 1/2 inch per year.  This fault creep is seen in only a few locations on earth, another being the north Anatolian fault in Turkey. 

Driving through Hollister, we saw sharply offset curbstones, drainage ditches and front porches, the result of decades of slow creep.  Following the damage from one neighborhood to the next, we found the fault line as it passed through each house to the one after.

We drove on to San Juan Bautista, the small spanish town that sits astride the San Andreas fault.  Blessed in the year 1797 by Fr. Fermin de Lasuen, mission San Juan was  completed and dedicated on June 23, 1812.  It was heavily damaged in the earthquake of 1906, which ruptured the fault line just to the east at the base of the hill by the cemetery.  The old mission has played many roles, one of the more interesting being the centerpiece of the 1958 Alfred Hitchcock thriller Vertigo, starring Jimmy Stewart and Kim Novak.

At last we came to the Cienega Valley and the DeRose vinyard and winery.  The winery is the latest of several wine buildings at that location since the mid 19th century.  It sits directly astride the creeping San Andreas fault, with the eastern side of the winery on the North American tectonic plate, and the western side on the Pacific plate.  A building inspector noticed the damage to the winery in 1956, and was followed shortly thereafter by teams of geologists and seismologists.  The wine itself is crafted under the careful supervision of winemakers Pat and Al DeRose and their families.  A wonderful antique car museum occupies one portion of the building.

As I reflect on those events, I find on the table in front of me a bottle of DeRose Syrah 2006, a fine vintage from the old dryfarmed vines, recalling fond memories of that time on the fault line many years ago.


Harjo D's picture

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