Forces Of Nature

In my previous article on the three major, unpredictable forces of nature — wildfire, wind and earthquake — in Anderson Valley, I focused on wildfire and wind and my experiences during my valley years, from the late 1950s to the late 1980s. As promised, this article will delve into the valley’s other force of nature: earthquake.

Despite proximity to the San Andreas Fault, Anderson Valley rarely experiences earthquakes. Unlike much of California, the valley isn’t bisected by earthquake faults, so shaking felt in the valley comes from substantial quakes occurring beyond its confines.

Still, every so often, Anderson Valley gets shaken. The quake I remember hit on the last day of seventh grade, June 6, 1962. The upper grades of grammar school, fourth through seventh grade, took over the old high school buildings (since torn down) when the high school moved into its current facility on Mountain View Road in the 1950s. Our seventh grade classroom was on the second floor of a small structure tucked behind the main building, with access via both a small bridge from the gym and a stairway from the back. The mostly unfinished bottom floor was used for storage.

Our textbooks for the year turned in, our teacher was reading “The Telltale Heart” by Edgar Allan Poe to the class when the building began shutter and sway. The classroom had rows of hanging fluorescent lights and these began to swing back and forth. Within a few seconds, they were hitting the ceiling on either side. By then, the long bell used to signal fire drills was ringing, and we were piling out the door and down the stairs. The shaking quit about the time the class reached the open ground behind the school. The buildings looked unscathed except for minor stucco cracks near the foundation. I don’t recall whether we were sent home early that day, but I am pretty sure our teacher never finished reading “The Telltale Heart!”

The quake turned out to be the largest centered in Mendocino County during the 20th century. Registering magnitude 5.2, it had an epicenter east of Hopland and was felt from Fort Bragg to Oakland.

Big quakes some distance away occasionally are felt in the valley, though it has been decades since the last one (probably the Loma Prieta earthquake of 1989, which — according the maps — barely registered). Neighbor Don Van Zandt’s recollection of how the 1906 earthquake whipped redwood trees back and forth so violently their crowns nearly touched the ground was included in “Neighbors,” my article in the August 5, 2013 Anderson Valley Advertiser. California’s official report on the 1906 earthquake stated half the chimneys in Boonville were thrown down and included observations by John Prather of Philo — town founder Cornelius Prather’s son — that many local chimneys were “broken off above the roof and in some cases turned quarter way around, clockwise. Glassware and pottery were generally broken and much damage was done in stores and farmhouses.”

One big earthquake really stood out during my research into this article. On April 14, 1898, a magnitude 6.8 quake with an epicenter just west of Mendocino struck shortly after 11 p.m. Chimneys were toppled in towns up and down the Mendocino Coast, the base of the Pt. Arena lighthouse cracked, four houses and a wharf collapsed in Elk (then called Greenwood) and roads buckled in several places. In Mendocino, many businesses were damaged, several one-inch and wider cracks in the earth opened, including one on Main Street that ran for nearly 100 feet and another next to the lumber mill that ran more than 200 feet, and nearly every gravestone in the cemetery either toppled or twisted around on its base. The quake was felt from San Jose to Eureka — which means Anderson Valley got rocked — and was strong enough to stop a train station clock in San Francisco.

Accounts of this quake left me puzzled. How come such a big quake located so close to Mendocino didn’t result in the town — with buildings made almost exclusively from redwood and heated with fireplaces — burning to the ground? Additionally, how was it possible such a large quake caused no fatalities? So I did some research and, while there is no definitive answer, a combination of factors may explain the odd outcome.

Two were weather related. Although I could not find data for Mendocino, March of 1898 may have been the town’s wettest March ever. The March 1898 rainfall total in San Francisco was 7.61 inches, which suggests Mendocino may have received more than 10 inches. In short, the wood buildings and shake roofs were saturated, and would not have caught fire easily. Then there was the weather immediately prior to the quake. On April 12, San Francisco recorded a high temperature of 87 degrees — downright hot. It is likely Mendocino experienced similar hot weather on that and succeeding days. While a few days of hot weather would not have dried out the wood buildings, it likely kept people from having fires in their fireplaces the night of the earthquake.

The other two were quake related. Approximately 22 minutes prior to the big temblor, there was a foreshock. Records don’t say how large, but it was firmly felt in Mendocino. As a result, residents almost certainly vacated their homes and were out of harm’s way when the main quake struck. Then there was recent quake history. On March 30, 1898, a sizeable quake hit near Vallejo and was felt throughout the surrounding region, including San Francisco. Damage at the Mare Island Navy Shipyard was so extensive, the U.S Congress appropriated $350,000 (the equivalent of $10 million today) for repairs. While that quake wasn’t felt in Mendocino, it was a major news story and may have made folks more cautious than they otherwise might have been when the Mendocino foreshock hit.

All this is supposition; we have no way of knowing whether these factors played into the lack of fatalities and fire damage from the 1898 Mendocino quake. Still, they provide an explanation for the otherwise inexplicable.

Interestingly, I noticed a magnitude 3.9 earthquake with an epicenter in almost the same offshore location as the 1898 Mendocino quake hit on April 11, 2012 and a magnitude 4.5 earthquake hit near Ukiah on September 25, 2012. So maybe Anderson Valley residents shouldn’t be too sanguine: the potential for a big temblor is always present.