Do Real Estate Agents Have to Tell You About This Kind of Thing? California Has Her Faults

It was the third weekend in November, and thus time for our last field studies excursion of the year. We headed into the Coast Ranges of California, braving rain and wind for a chance to investigate the San Andreas and related faults, and to explore one of the lesser-known gems of the National Park System, Pinnacles National Monument. One of our first stops (and indeed a stop for practically every field class that ventures forth into Central California) is the town of Hollister, south of San Jose, and sitting right on top of the Calaveras fault.

The Calaveras fault is an offshoot of the San Andreas, separating from the main fault a few miles south of town. The Calaveras is quite clearly active, as can be seen in these photos. The fault is well-known for creeping rather than sticking and slipping (and producing ruinous earthquakes).

The fault moves at rates as high as half an inch per year, although the rate is highly variable. The fault runs through numerous homes, and the movement is slowly tearing the foundations apart. Every decade or so homeowners must lift the houses up and replace the foundations.

The side of the porch has shifted to the right, away from the steps

The fault is easily traced in the neighborhoods between 1st Street and 6th Street at Dunne Park. I've noticed that folks living on the trace of the fault barely look up from their porches as classes walk down the street following the fault zone. A few are proud enough of their notoriety that they will come and describe what they've been doing with their faulty houses.

Our trip route took us south of town, to where Cienega Road intersects and then follows the San Andreas fault. Beyond the Hollister Hills State Recreation Area, one reaches the DeRose Winery, another famous fault locality. The winery was built directly on the trace of the fault, and has been destroyed twice by creep along the San Andreas.

The owners have always been kind to our students, allowing us to sneak through the wine-tasting event to have a look at the interior walls, which have been offset by several feet (below).

 The wood post and the cement slab started out together...

The water-course at the south end of the winery is one of the most famous drainage culverts in existence because of how it has been offset by the fault (I forgot to get a picture this year; this is last year's version).

I don't know if realtors have to disclose the fault problems of home-buyers in Hollister, but if the DeRosa owners ever have to sell their winery building, they'll have a hard time hiding their fault...there is a brass plaque in the middle of the building declaring it a Registered Natural Landmark by the Department of the Interior!

The other San Andreas fault locality for our trip is on Highway 25 where the road is traversed by the fault. The road was completely repaved in the last year or two, but if you look carefully, you can see that the fault is already at work tearing the road apart again.

 For a sense of comparison, below is a shot from 2003...

 ...and a shot from 2008 after a patch job.

We had an audience at our stop...a gang or rafter of dinosaur descendants trying to avoid being the main course later this week!

California Has Her Faults; Here's One of Them...

I didn't think it would take long for the geologists among us to figure out that we looking at a fault rupture in yesterday's "minor mystery photo", and I wasn't disappointed. These en echelon cracks are called riedel shears, and are the first cracks that appear as a solid material is being put under (in this case) lateral stress. There was no earthquake; this is a section of the fault that is creeping, meaning that it is moving constantly without building up enough stress to produce large earthquakes.

This isn't just any fault; it is the fault in California, the San Andreas, which forms part of the boundary between the Pacific and North American plates. The section we visited on Saturday is between the town of Hollister and Pinnacles National Monument, south of the 200 mile long rupture from the 1906 quake in San Francisco. How much does the fault move every year?
A clue is provided by a shot I took in 2008, immediately following the road repairs. No damage was yet visible, and none in 2009 either. I was a little disappointed in 2008 to see that the road was fixed, as it took away one of the more visible bits of evidence of fault motion. The picture below is how the road appeared in 2002. The first time I saw the fault crossing in the 1990's, the fracture was a straight break crossing the highway, with a big bump. Thus, it's been repaired at least twice in twenty years

Without human developments, the year-to-year movement would be hard to see because the subtle effects are obscured by weathering and erosion. In the pictures below (about 8 miles south of our damaged highway) the old fencing shows several feet of offset.

Probably the most famous evidence of movement on the creeping segment of the San Andreas is the De Rosa Winery warehouse (formerly the Almaden Winery). The winery was first constructed in the 1800's and has been rebuilt twice after the building foundations failed. The current building is also being ripped apart, along with a culvert that has been photographed many times by visiting geologists (thrilled, no doubt, by the fact that they can combine their field research with wine-tasting!). The winery owners study geologists too; in this article, they are quoted as saying "Their pants always have zippered pockets...The khaki pants and the funny hat, and you know it's a geologist."

I am traveling this Thanksgiving, like so many others, and will have infrequent web access (my phone is only semi-smart and only makes phone calls). I hope you all have a fine holiday, and that you have many things to be thankful for. Below is one dinosaur descendant that is feeling thankful that it won't be eaten this holiday, as it lives in Pinnacles National Monument and enjoys protected status.

Rhyolite in the California Coast Ranges? And Happy Thanksgiving...

I only provided one picture of Pinnacles National Monument in California's Coast Ranges in my previous post, and it showed none of the scenery that makes the park a special place. So here are two views of the 22 million-year-old rhyolite composite volcano that was erupted, sliced in half by the San Andreas fault, faulted into a graben structure, exhumed by uplift, and eroded by water and wind and mass-wasting into a beautiful parkland.

The first photo is a view from the High Peaks Trail, a marvelous 5 mile loop through the heart of the park. The walk across the ridgeline is just stunning. In many places, footholds had to be scooped out of the rock to provide access, although the exposure level is not too frightening (nothing like Angels Landing in Zion, for instance). On a clear day, the far ridges extend forever into the distance, while the giant monoliths of rhyolite dominate the foreground. This hike, along with the trail to Delicate Arch, and the climb of Angels Landing, is one of my favorite hikes in the world.

The second shot is a view of the previously mentioned high peaks from the perspective of the south end of the park on the trail to the Chalone Peaks. The High Peaks Trail winds along the spine of the ridge in the center of the photo, and has connecting points to trailheads on both sides of the park (no roads cross the park, so one must choose to visit from the west or the east side).

The third photo is one of the wild denizens of the park, an old Tom Turkey. I have a feeling this bird would have issues with a certain recent vice-presidential candidate. I have seen a lot of wildlife in the park, include a huge flock of wild turkeys, four or five California Condors, huge numbers of woodpeckers, the standard deer and various rodents, and my favorite, a huge bobcat. The cat was hanging out near the edge of the campground near the road, and as we approached on the highway, what I thought was a feral kitty-cat seemed to grow larger and larger until I finally realized what it was and grabbed for my camera. Too late of course. And I can't help but look for the cat at the same spot every time I pass by during subsequent trips, camera ready in hand.

I hope everyone in the geoblogosphere has a fine Thanksgiving, even if you are not in the particular country that celebrates the day. Times are toughening up for many of us, but here's wishing that we all weather the storm, and that the job situation brightens for those of you who are between jobs and searching for employment. Best wishes to all of you.