Category: StreetSmartNaturalist

A Streetcar to Subduction

I wish I could lay claim to coming up with the title for this post, but I cannot. The title, officially Streetcar to Subduction and Other Plate Tectonic Trips by Public Transport in San Francisco, is from a wonderful paper by the late Clyde Wahrhaftig. Originally written for the AGU in 1979, the paper was updated in 1984. Wahrhaftig described six trips that one could take by public transport around San Francisco to see the area’s geology. The rare and expensive booklet (six copies were available on amazon.com from between $60 to $130) is a pleasure to read, not only for the geology but also for Wahrhaftig’s insights on history and architecture.

The J Church line is the so designated Streetcar to Subduction. With a little effort you can see pillow basalt, sandy turbidites, and radiolarian chert, basically a microcosm of typical oceanic crust. You can learn about how two high school student broke into the supposedly impregnable New Mint Building, just weeks after it opened, and you can learn to identify and avoid poison oak. On another route Wahrhaftig gives an introduction to San Francisco architecture and on one more he reveals how residents saved their houses during the post-1906 earthquake fire by soaking cloth in wine and spreading the material on their roofs. He also shows where to see serpentine throughout the city.

Born in Fresno, California in 1919, Wahrhaftig was an avid outdoor explorer and field geologist. He died in 1994; a thoughtful obituary is available on the UC Berkeley web site. He didn’t drive and often eschewed conventional means of travel. As someone devoted to making geology accessible to everyone, he put together his now legendary guides to San Francisco rocks. In addition to Streetcar, he also wrote A Walker’s Guide to the Geology of San Francisco, which does contain one walk that focuses specifically on the building stone of the city.

Gary Cooper and the Stones of San Francisco

With the upcoming AGU annual fall meeting, I want to look at some of the building stone used in San Francisco.  Despite the area’s abundant stone, the earliest fireproof granite building used stone quarried, cut, and fitted together in China.  Known as the Parrott Block, it was built in 1852.  The blocks had been labeled with Chinese characters and shipped to San Francisco, to be assembled by Chinese workers.  The three-story building survived the 1906 earthquake and fire but was razed in 1926 for the Financial Center Building, now remodeled as the Omni Hotel. 

Various rock trickled into San Francisco in the following decades. By the end of the century two of the most prominent were a sandstone quarried near Sites and a granite from Raymond.  Sites is about 100 miles north of the bay area, in the Sacramento Valley, whereas Raymond is 150 southeast in the foothills of the Sierras.  Both rocks reached the city by train. 

Colusa sandstone quarry – From: http://quarriesandbeyond.org/states/ca/quarry_photo/ca-colusa_photos.html

Two quarries in Sites provided stone.  A. D. Knowles opened his quarry in 1886, followed in 1890 by the John McGilvray Stone Company.  Known in the trade as Colusa Sandstone (the town of Colusa is about 25 miles away), the rock comes from the Upper Cretaceous Venado Formation, a several-hundred meter thick layer of submarine fan deposits.  They are part of the Great Valley Group, tens of thousands of feet of muds, silts, and sands that accumulated in a forearc basin found between the Sierra Nevada magmatic arc and the Franciscan subduction complex. 

The Ferry Building was the first great structure made of Colusa rock.  Other well-known buildings are the St. Francis Hotel, Music Temple in Golden Gate, and the Flood Building.  The stone was also shipped to Hawaii.  It is generally bluish gray or buff, though a recently opened quarry about one mile north of the original quarries markets the sandstone as a brownstone.  Like other sandstones during fires, the Sites rock spalled heavily during the post-1906 earthquake infernos. 

Raymond Granite Quarry – 1905 — From: http://www.sjvls.org/photoheritage

The Raymond granite quarry opened in 1888 on property locally known at the time as Dusy’s Rock Pile.  Light gray in color, the Raymond rock is classic, Sierra Nevada subduction zone granite, and is now sold as Sierra White by the quarry’s present owner Cold Spring Granite.  Raymond granite was used in the San Francisco Civic Center, City Hall, Palace Hotel, and numerous buildings on the UC Berkeley campus.  The new main San Francisco library, built in 1996, also has a granite façade from the Raymond quarry. 

The stone, or at least the quarries, achieved a bit of notoreity in 1949 in the movie adaptation of Ayn Rand’s The Fountainhead.  At a low point in his career, architect Howard Roark, played by Gary Cooper, retreats to a job in a quarry.  The quarry in the book is in Connecticut, but since the film was shot in California the Raymond quarries had to stand in for Connecticut.  Although limited, the scenes in the quarry with Cooper and Patricia Neal are some of the movie’s most famous and controversial because of their sexual imagery.  And for those inclined to stone, the shots do a fine job of depicting quarry technology.