An Iconic Bit of the Calaveras Fault in Hollister is Gone (But it will be back)

Corner of Locust and Central Avenues in 2016

I go on field studies trips year after year, and my camera is always around my neck, to the amusement of my students. They sometimes wonder why I would take pictures of things I already have dozens of pictures already. I sometimes wonder the same thing when I am trying to track down a specific shot from my archives of tens of thousands of pictures. But for a teaching geologist, there is a very good reason:

Things change.

Sometimes it is sudden, like a flood in Yosemite or on the Tuolumne River that actually alters the look of a landscape. It's nice to be able to catalog before-and-after views of a place. But in others, it is because of the incremental geologic changes. That's especially true with a couple of faults in Central California, the San Andreas and the Calaveras.

Corner of Locust and Central Avenues in 2013

Yesterday I updated the spot on Highway 25 near Pinnacles National Park where the San Andreas fault crosses the road (and I deeply appreciate the widespread response, especially on Twitter). The spot visibly changes every year. For decades, geologists have also been tracking the creeping of the Calaveras Fault in downtown Hollister. Generations of geology class field trips have walked several city blocks, tracking the fault as it offsets streets, sidewalks, curbs...and houses! I hope that all who do so remember to stay on sidewalks and not become nuisances to the residents. They have enough to contend with when you think about it.

The corner of Locust and Central Avenues in 2001

One curb has been iconic; it's been an illustration in any number of textbooks and PowerPoint presentations. The corner of Locust and Central Avenues is offset by the Calaveras Fault adjacent to the crosswalk, so it can be observed easily without bothering residents. It's one of the most vivid examples of right lateral offset imaginable, and if one knows the age of the sidewalk, the changes can be used to calculate the yearly rate of movement on the fault. The break is not a perfect measure because the deformation is spread out for several yards on both sides of the break (note how the sidewalk is curved in the pictures above).

So you can imagine my surprise on Saturday to find that the iconic curb disappeared sometime last year. It was for a good reason, as the city put in a wheelchair ramp, but it was still a shock. I was disappointed for a moment for my students until I realized that for the first time in 15 years, we have a brand new baseline of fault movement. Because as surely as the curb was offset before, it will continue into the future. We'll be watching for the first of the tensional cracks in the concrete, eventually to be followed by total rupture and offset curbs.

Corner of Locust and Central in 2017

Geology never stops.

Getting a Creepy Feeling in Central California: A "Transforming" Experience

Faults can be active without producing major earthquakes. When the fault plane is not locked by frictional resistance, the sides of the fault can slide past each other without building up the stress that leads up to huge quakes. In Central California, there are several faults creeping on a more or less consistent basis year after year. They are close enough to each other that they can be easily visited in an afternoon. That is exactly what we were doing last Saturday.

The town of Hollister is bisected by the Calaveras fault, and numerous homes, sidewalks, and streets are slowly being torn apart by the constant movement, amounting to as much as 14 mm/year (0.55 inches). The embankment in the photo above appears in a number of geology textbooks as an example of fault motion.

The foundation for this 1920s vintage garage has also been seriously damaged. We've been visiting the spot for 28 years. It will be disappointing when they finally decide to renovate the building!

Probably the most famous example of fault creep in the region can be found at the DeRose Winery a few miles south of Hollister. The fault is far more active, with yearly offsets amounting to as much as 25 mm/year (1.0 inches). One can get a sense of the magnitude of the motion by comparing Saturday's image to one taken half a century ago (below) 

Source: NOAA/NGDC, University of California, Berkeley.

The DeRose Winery has changed hands a number of times in the last 160 years, and the owners of the place in the 1980s kind of let it go (I believe they were even trying to produce tiger prawns in the old wine vats for time). The current owners are a treasure. They recognize the scientific value of their property, and have been clearing weeds from the drainage that threatened to completely hide the iconic symbol of right lateral strike-slip motion. They have also never refused us entry into the warehouse where offsets accumulating since 1948 are nicely exposed in the walls, even when formal wine-tasting has been going on.

All of these incredible exposures are easily accessed. If you are ever in the vicinity of Hollister or Pinnacles National Park, don't miss the opportunity to lay your hands on a major transform plate boundary!

"A City Divided!" "Rift Tears City Apart!" "Slip-Sliding Away!" "Creepiness on the Calaveras"... I Give up: "Calaveras Fault in Hollister"

Blogging has certainly given me some perspective on life at newspapers or internet news services. The title of a piece is all you've got to convince people to click through. I am constantly irritated beyond words at the clickbait out there: "She thought no one was looking. You won't believe what happened next". That kind of thing. And yet I couldn't help it. How many ways can you say a fault can be seen cutting a city in half?

If you have ever had a geology class in the Bay Area or Central Valley of California, there is a chance you went on a field trip to see the Calaveras fault where it passes through the Coast Range town of Hollister. The Calaveras, a close cousin to the better known San Andreas fault, runs through the city, and it is slowly tearing neighborhoods apart. Like the San Andreas in this region, the fault is creeping instead of storing up seismic stress, moving perhaps a quarter inch per year. Curbs, streets and foundations are all slowly cracking and moving apart.

The creep has progressed to the point of seriously damaging some of the beautiful Victorian-style homes built in the 1920s and 1930s. Several have been repaired by lifting them up and replacing the foundation beneath them.

Street and curb repairs have been ongoing, with new patches showing up on a constant basis.

These are textbook examples of the effects of fault creep. Literally. Pictures of many of these homes and sidewalks show up in geology textbooks (including one or two of my pictures) as examples of the phenomenon.

The neighborhood has been the focus of hundreds of field trip visits over the years. I would hope that the students recognize that people live in this neighborhood, and thus respect their privacy and property. There is more than enough to see from the public sidewalks, streets and parks. 

No trip in the region is complete without a visit to the DeRose Winery, especially on wine-tasting day (and no, none of my students imbibed on Saturday)! The winery, the oldest in California, is several miles south of Hollister on Cienega Road. The San Andreas fault runs right through the winery warehouse and is slowly tearing the building apart. A culvert on the south side of the building shows very well the continuing offset along the fault.

Compare the same culvert as seen in 1961...

Source: USGS

I want to provide a shout-out for the owners of the DeRose Winery. Whenever they've been open on Saturdays they've allowed our students to walk through the inside of the warehouse to see the effects of faulting on the building. It's a privilege to be able to do this, and it is greatly appreciated. Follow the links above to learn more about their operation.

If your travels ever bring you to central California in region around Monterey or Santa Cruz, it's not hard to find your way to Hollister. It's worth your time!

It was the fault of no one, or maybe it's everyone's fault...the San Andreas and Calaveras faults in Central California

Central California has a lot of faults. One of them is a proclivity for bad geology puns. But it also has a great many exposures of active faults available for viewing in the space of an afternoon. The San Andreas, California's most famous fault cuts through the region, and the Calaveras fault lies a short distance to the east. It merges with the San Andreas north of Pinnacles National Park.

We became familiar with our faults today during our field trip between the town of Hollister and Pinnacles National Park in the California Coast Ranges. The faults are both actively creeping instead of building up ominous levels of stress. Earthquakes are a little bit less of a concern here, although some particular homeowners have problems with their foundations.

These are famous fault exposures. Photographs of these offset features have been published in textbooks all over the world. They are also easily accessible on public streets and parks. It is fascinating to watch the Earth in action.

The Calaveras fault is an offshoot of the San Andreas, extending north for about 70 miles from the vicinity of Pinnacles National Park. It has produced several magnitude 6+ earthquakes in the historical period, including a 1911 event in Morgan Hill with a magnitude of 6.5, and another quake in 1984 of magnitude 6.2.

A newly paved street at Dunne Park in Hollister

Dunne Park on Sixth Street in the town of Hollister is a good starting point to search out the fault zone. If you visit, please be respectful of the property lines. The people here see a lot of geology students, and while residents are almost always polite and even talkative, it would be sad to see "No Geologists Allowed" warnings springing up like "Neighborhood Watch" signs.

A short while later we headed south on Cienaga Road past the Hollister Hills Off-Road Vehicle park to an old winery. The warehouse was built directly on the creeping fault zone, and is slowly being ripped apart by the inexorable motion (two previous warehouses were apparently destroyed at this site as well). In the picture below, the cement wall was once connected to the wall with the blue tarp. They are offset by several feet. The dark plaque a bit to the left is a marker noting the establishment of the winery as a National Landmark.

The owners of the winery are friendly and have never refused our students the opportunity to look at the fault damage in the building, even when important functions were in progress. They are to be commended for maintaining access to this important site.

The drainage culvert on the south side of the building is probably one of the most photographed fault offsets anywhere.

Our last fault feature of the day before arriving at Pinnacles National Park was a spot on Highway 25 where the San Andreas fault crosses the pavement. It has been patched many times, and in the last year or two, the highway was completely repaved. On our previous visit the road showed no evidence of motion, but this year we could see modest cracks forming.

I would have felt really bad if we had set off a major quake by jumping on the fault zone, but then again it sure would have been neat to stand on the fault as a large earthquake commenced.

Back to the beaches in coming posts!

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!

Hey! It's not my fault! It's San Andreas' fault...A Creepy Story

DeRose Winery drainage culvert in 1961 (courtesy of USGS field guide)

Quick, what's the difference between the pictures above and below? Well, OK, besides the growth of vegetation and the passage of 50 years?

DeRose Winery drainage culvert yesterday, courtesy of me...

If that drainage culvert looks like it has moved several feet in the last fifty years, you would be right. It was built right over the San Andreas fault, and in this part of California the San Andreas creeps a little bit each year (this is a good thing; this part of the fault doesn't build up stress, so it doesn't produce large earthquakes).

The drainage culvert is a famous locality that is visited by hundreds of geology students every year. It is located at a winery about eight miles south of the town of Hollister in the central California Coast Ranges. That's what we were up to yesterday, exploring the San Andreas and Calaveras fault zones with my geology students.

As I recall the story, the winery was first constructed in the 1800's, but for some inexplicable reason, it fell apart. It was rebuilt and then fell apart again, and then was constructed once again at the present location in 1948. When the building started showing signs of stress again, an investigation in the late 1950s led to the conclusion that it had been built on the San Andreas fault, and that the fault was moving around 0.5 inches per year.

As can be seen in the picture above, the building is suffering serious damage again. We have been coming here on field trips for twenty years, and something different can be seen every year as new patches, repairs, and repaved roads can be seen. But in all those years, there was something we had never done before...we had never gone inside. By a quirk of scheduling, we arrived earlier in the day, and stumbled onto a wine tasting event. We headed inside to have a look around (note to my dean: we did not stumble out...no one went wine tasting in our group!). The damage inside actually looked worse than what we could see on the exterior.

It's not like they don't know the building is on the San Andreas...that bronze plaque on the wall in the picture above is a 1965 designation of the site as a Registered Natural Landmark, and there is a map of the San Andreas fault in the poster to the right.

The wood post on the left was once even with the concrete wall on the right. The concrete has moved to the right, making the San Andreas fault a right lateral strike slip fault. I've outlined the sense of motion in the picture below.

I'm wondering if any of the structural geologists out there can make sense of the fracture patterns of the the concrete on the floor in the picture below?  It looks to me like there might be some conjugate fractures and rotation among some of the chunks.  I appreciate that the owners seem not to have fixed that part of the floor (I wonder if that was a stipulation of being declared a national landmark?)

The north wall has some serious warping problems (below). The doorway is nearly impassable as the wall in the foreground is shifting more and more to the left.

I've written about this trip a few times. The point where the San Andreas fault crosses Highway 25 that showed clear signs of fracturing on our trip last year (blogged here) has been repaved, so we'll keep an eye on it for changes over the next few years.

It's easier than you might think to see the San Andreas and Calaveras faults for yourself. There are several good road guides in books and online. An excellent one by the U.S. Geological Survey can be accessed here:  http://pubs.usgs.gov/bul/b2188/b2188ch6.pdf

There were some pretty sights at Pinnacles National Monument. More in the next post!