Hollister’s Creepy Problem
Hollister is an unassuming small California town (population 35,000) located about an hour south of the SF Bay Area in the countryside east of Monterey Bay. The town has no relation to the popular clothing label of the same name.
Hollister is exceptional in one very surprising way though. The city sits atop the Calaveras fault, a branch of the much more famous San Andreas fault. It was this fact that prompted me to visit during a trip to California late last summer.
Most faults in the San Andreas system are stuck or “locked.” That is, due to friction and contact among the rocks deep underground, they resist tectonic movement for long periods of time (decades or centuries) until the accumulated forces cause a sudden break or rupture. This sudden rupture, in which the stuck fault may move many feet in a few seconds, is felt on the surface as an earthquake.
Many faults in central California— including the Calaveras — behave differently. Instead of being stuck (and moving only during major earthquakes), they creep continuously, moving a very reliable fraction of an inch every year. As a result, the city of Hollister is being torn in two in a very slow-motion way. The trace of the fault can actually be seen throughout the city by observing the behavior of sidewalks, curbs, streets and even houses. The creep itself is continuous but the rate is not. Some years seem to be a bit faster and some slower, but the overall average over the past few decades seems to be about 1/5 to 1/2 of an inch per year (4–12mm).
Since we’re not talking large catastrophic earthquakes here, but just inexorable creep, the damage is slow, cumulative and relentless. Curbs are gradually stressed and then broken over a period of years. Houses warp and fall out of plumb at the rate fingernails grow. Owners learn to live with gradually sagging walls, shifting foundations, cracked sidewalks and sloping floors — and make repairs when they must. One owner I talked to said he was very aware of the fault-creep issues when he bought his house, and never really second-guessed his decision. It’s just a fact of life in certain Hollister homes, and something owners accept as a quirk of the area.
There’s something irresistibly fascinating about fault-induced ground movement. I’m riveted by the idea of surface evidence of such movement; places where surface deformation and displacement are clearly visible at the surface. There’s no place better to see multiple instances of such movement than this lovely neighborhood on Hollister’s near-west side.
In this article, I’ll share some photos I shot in Hollister during my visit, and compare them to similar shots from past decades, in an effort to document the progression of the fault-creep. Many of these shots were taken from Joe Dellinger’s excellent “walking tour” of Hollister located here. Photos labeled as “2018” were taken by me. Any earlier photos come from Dellinger’s tour website or were obtained elsewhere as labeled.
My photographic tour will have a total of 5 stops, as illustrated on the Google map below.
1. The Locust St. Curve
In the three photos below, showing a period of 52 years, note the deformation of the curb on the left (south) side of Locust St. Though my angle in the third photo was not exactly the same, it is evident that the distortion increased significantly from 1992 to 2018.
In the thee dated photos of the Locust Curve, note the movement of the curb. The bend has the curb making an “S-kink,” causing the more distant part of the curb to appear to move to the right, relative to the observer. This is the defining movement of a “right lateral” fault. If you stand looking across the fault, the far side will always appear to move to the right.
2. 359 Locust St.
The house at 359 Locust St. seems to have missed being built directly on top of the fault by just a few feet. The fault instead bisects the front yard. The sidewalk leading to the front porch is the main focus. The Google Satellite view here clearly shows the “bend” in the sidewalk.
The shots below show the sidewalk in detail, over a period of 33 years.
How is the house affected? According to the author of the walking tour page, which is the source of the 1985 photo, the homeowner claims there are no problems with the house or the foundation. But take a look at the 1985 photo and then the 1989 and following photos: The entryway has been remodeled since the 85 shot. While there are lots of reasons for a home remodel, it’s not a stretch to speculate that the creep movement hastened the need for home repairs here. Next time I visit, I hope to interview the owner and see what I can learn about the house’s history.
If you follow the trace of the fault (see Google Maps Satellite photo above) through the yard at 359 Locust, it would next cross Fremont Way (actually an alley) and then intersect the next building to the south. I didn’t know about this when I visited, so I don’t have my own picture, but the picture below was captured from Google Street View:
3. Fourth St. Retaining Wall and Sidewalk
As the fault continues its trace toward the southeast, it appears to pass directly underneath the house on the NE corner of Locust and San Juan Rd.(San Juan is also labeled as Fourth St., so for the purposes of this article, I’ll use “Fourth.”). The house is located at 588 Fourth St.
First, the retaining wall and sidewalk directly in front of 588 Fourth St.
It’s hard to tell how many times the wall has been painted and/or repaired in the 52 year span of the photos. It’s clear in the 2018 shot that the corner nearest the camera is being badly pulled apart and the entire front section appears to be sagging toward the sidewalk. The skew in the centerline of the sidewalk has clearly progressed over the years in the expected right-lateral direction.
What are the effects to the house? With the fault trace passing directly below 588, surely there must be some interesting effects and repairs over the years? Sadly, the only other photo of this house I can find is the Rocdoc’s shot from 2015:
The sidewalk directly across the street from 588 is the subject of the following photos:
This series of three photos of the Fourth Street (south side) sidewalk, just across from 588 Fourth St, show what may be the most dramatic surface deformation in the Hollister area. Sighting down the elevated curb on the right side of the sidewalk, the skew is evident as a simple right-lateral jog in the 1966 image; has progressed significantly in the 2004 image (with a slight break just this side of the jog), and by the 2018 image, the whole curb is a twisty mess. Similar deformations of the sidewalk are evident.
4. Houses on Fifth St.
Two houses on Fifth St are of interest. The fault appears to pass almost directly between the houses at 570 and 558 Fifth St:
The house at 570 is probably my favorite spot in Hollister. At first glance, you might not suspect a thing and just keep walking. But if you’re in Hollister because you know the fault runs just under the town, you might stop to take a long look at this house. Once you see the leaning and skewing, you can’t unsee it. Then you start to see other things, like the little dip in the elevation as you proceed down the sidewalk in front if it, or the warp that develops in what otherwise might have been a perfectly straight little picket fence.
While I was walking up and down Fifth St, obviously looking at this house and the surroundings closely, I was approached by the owner of the house immediately to the east — Randy. With no introduction he said: “if you like that, you gotta see this,” and brought me over to his house. He didn’t need to ask me what I was doing there. The residents of this particular section of Hollister are very accustomed to strangers with cameras. Here is Randy’s house (558 Fifth St):
Randy is not a geologist, but his knowledge of local geological circumstances is pretty thorough (he’s posing by his rock collection). Though they have lived in their house only 4 years (as of my visit), they had a thorough inspection done by an engineer before they bought it. The engineer reported that their foundation is unusually thick and the walls contain an inordinate amount of concrete. He speculated that the builder knew about the fault and was planning for the future. He reports that the wandering roofline had been completely rebuilt at some point prior to his purchase of the property.
5. Adjacent to Dunne Park along Sixth St.
Along the north side of Sixth St is another landscaped retaining wall. Photos below document the creeping deformation. The progression distortion of this low wall is one of the best examples of the fault-creep’s relentless nature.
In the street directly in front of this wall is a section of curb that has been often photographed:
These five sites are just a taste of what’s sitting right there on the surface in the town of Hollister. For all their apparent sexiness, earthquake faults are generally pretty invisible and boring. But occasionally geology bubbles up in a way that is interesting, provided you have a chance to really take a look. There are only a few places in the world where surface deformations resulting from fault movement are clearly visible. Hollister is one of the best.
There’s a lot more to Hollister’s seismology to be seen and discovered (to say nothing of its great library, good coffee shops and restaurants). If you ever get a chance to visit, I hope this guide will provide you with a starting point to have a look around and be amazed.
If you have any historic photos of Hollister that show other views of any of these sites, or others, please let me know in the comments below.
Below are a few links for further reading:
Joe Dellinger’s “Walking Tour” of Hollister that originally piqued my interest in this topic— Dellinger’s webpage on Hollister’s fault creep is the gold standard of the type of re-photography I have tried to present. Thanks to Joe for his original work over three decades ago!
Field Trip Guide to Greater San Benito County
Article in local press by a retired science teacher from Hollister
Daily Beast article with some thoughtful prose
Article in local press that sheds light on building and zoning permit issues
