Cute to a Fault: Teaching Kindergarten on the San Andreas Trace, Part I

One of my more interesting experiences since coming to the Golden State was teaching Kindergarten. For the school year 2007-2008, I accepted a Kindergarten assignment at San Juan School in the beautiful town of San Juan Bautista.  Located on Nyland Drive, San Juan is a K-8 school and is part of the Aromas-San Juan Unified School District.  This particular assignment was only my second full-time year, and in the end proved one of the most exhausting years of my professional experience.  For one thing, I was living in Merced at the time so I had a one-way commute of almost two hours (admittedly, the commute was via CA 152 through Pacheco Pass, so as someone interested in geology I couldn’t complain too loudly; not everyone gets the pleasure of a daily drive that includes numerous road cuts through a Mesozoic subduction zone); there were times when that extra three or four hours added to my work day was unwelcome.  For another thing, teaching Kindergarten-aged kids is the most energy-intensive activity in the teaching profession bar none, and even though being around them was emotionally refreshing, it was physically exhausting.  They were a really cute bunch and they caught my heart on a daily basis, but you have to be “on” every second you are around them, and their 10-second attention-spans left my head spinning by the end of the day.  By the end of the year, I knew Kindergarten was too young an age group for me in terms of future assignments; my current grade ranges are anywhere from Sixth through Ninth.

The coolest thing about the year, however, was that my classroom, Room 28, was about one hundred meters west of the main trace of the San Andreas Fault.

My classroom is circled in blue (photo courtesy of Geology Cafe.com)

I spent nine months working forty-hour work weeks practically on top of one of the most famous and most studied geological features on the planet.  In the words of my current group of students, it was “hella sick.”  Needless to say, I did not neglect the opportunity to become more familiar with the Fault and with some of the geology of the surrounding region during my time there; several free afternoons meant for “prep time” were spent exploring, especially in the early autumn and spring when the days were fair.  When weighing “Zoophonics” against tectonics, the outcome was never in doubt. 

The first avenue of exploration was of the fault trace, itself.   As the photo above shows, the fault trace forms the eastern/northeastern border of the town proper, beyond which lies the cultivated flatland of the San Juan Valley.  And it is really flat; about 240,000 years ago, massive landslides caused by movement along the Fault blocked drainage of both the San Benito and Pajaro Rivers into Monterey Bay.  The resultant Lake San Benito (as well as a later, smaller, longer-lived lake, Lake San Juan) flooded the San Juan Valley, and although its waters eventually drained away it left a thick, even layer of alluvium that buried the valley’s original features and made some of the richest farmland in the world.  And that illustrates one of the central facts of the San Andreas Fault: it is not the actual physical traces of the fault, itself, that are impressive (with rare exceptions, they almost never are), it is the impact it has on its surrounding topography that is profound.

When the Franciscans founded the mission of San Juan Bautista, they chose the flat surface at the top of a gentle slope as the site upon which to build their church and other mission structures, giving them as it did a view over the flat of the valley.  Unfortunately, what they could not have known was the gentle slope was a fault scarp; they were building their mission right on top of the main trace of what would later be named the San Andreas Fault. 

This has had some unfortunate consequences over the last two centuries---founded in 1797, the original church was heavily damaged by earthquakes in both 1798 and 1803, after which a new church was planned.  The new church was designed to be stronger and heartier to prevent earthquake casualties and damage, something which was subsequently forgotten in California until after the hard lessons of 1906 were learned.  Even with the “earthquake engineering,” the church was damaged (but survived) strong earthquakes in 1836, 1838, and 1868.  It was heavily damaged in 1906 (but rebuilt), and retrofitting enabled it to ride out the 1989 Loma Prieta quake with minimal damage. 

Because of its location along the Fault and its tendency to experience quakes, and because the study of quakes and faulting really took off after the 1906 disaster and subsequent Lawson report, the USGS chose San Juan Bautista to place a monument commemorating its centenary in 1979. 

It’s a charmingly understated monument to an organization that has monitoring stations, laboratories, and staff that has contributed to understanding of the Earth and its processes to such a large degree in its short life span. 

The Earthquake Walk not only follows the old El Camino Real as it passes the Mission, it lies on the fault scarp.  The stairs in the photograph descend the scarp, itself, and stepping down them and walking the path allows you to experience treading on a strike-slip fault with three different directions of movement relative to each other.  On the top of the slope before descending, the movement is to the north and west relative to the Valley floor at the base of the slope.  There is also vertical movement; the hilltop where the Mission is perched is over 70 ft. above the surface of the Valley it was once level with (vertical displacement was documented here after the 1906 rupture).  Of course, it hasn’t gained that much displacement in historical time; it accumulated over the last 20,000 years or so.  Still, it’s a pretty impressive impact over what (in terms of geological time) amounts to the blink of an eye.

Other than the Walk there are other traces to be found in San Juan Bautista but they are very subtle, and as is to be expected the damage of previous fault ruptures has been repaired in subsequent years.  The people of the town are not unaware of the significance of their location; there is a restaurant right on the scarp called The Fault Line, and the town boasts a first-class mineral shop called TOPS/Jan’s Rock Shop which hosts Fault Walks.  Even without such obvious clues, it is impossible for the town’s population to ignore the temblors the town experiences.  Indeed, one afternoon while sitting at my desk doing class prep after the kids had gone home, I experienced one such that was at least 3.5 on the Modified Mercalli Scale.  While it was not my first quake experience, it was my strongest and coolest to date and I enjoyed it thoroughly. 

Sources

Jenkins, Olaf P. Plesitocene Lake San Benito. California Geology, vol. 26, No. 7, July, 1973.