Secret of the Stones

Whenever I ride my bike to work, I come across a semi-circle of what appear to be old cobblestones at the intersection of Frederick & Shrader Streets.

Frederick & Shrader Stones

Frederick & Shrader Stones

I never thought much of it until I noticed a full circle of similar stones on 13th Street, at Folsom, near Rainbow Grocery.

13th & Folsom Stones

13th & Folsom Stones

13th & Folsom Stones

My curiosity was piqued. What do they mean? Why are they there? Are they the remnants of an ancient civilization, a decorative flare from a bygone era of well funded city government, or simply the remains of an old cobblestone street?

An e-mail to the San Francisco Department of Public Works solved the mystery. Chris McDaniels of the DPW quickly responded to my query:

“The cobblestone circle in the roadway is there to identify an underground San Francisco Fire Department water storage tank or cisterns. In emergencies, the SFFD rely on these indicator to assist in fire fighting when hydrant are non operational. The tank hold several thousand gallons of water and are installed at various location around the City. Modern cisterns use brick instead of cobblestones.”

As to the cistern at Frederick & Shrader, DPW Mechanical Engineer Michael B. Smith went on to say:

“Our records indicate it was constructed in 1908 of reinforced concrete and has a capacity of 75,000 gallons.”

He also sent me these fascinating DPW cistern construction drawings:

Frederick & Shrader Cistern Plans

Cistern Ring Construction Guidlines

The first document appears to be the original plans/work order for the Frederick & Shrader cistern dating back to 1909/1910.  The second is a somewhat more recent diagram from 2007 outlining basic cistern construction guidelines.

So there you have it! The Secret of the Stones. Hopefully they’ll never be needed, but it’s good to know they’re there.

Many thanks to Chris & Michael of the SFDPW for making this post possible.


Filed under General, History, Streetscape

8 responses to “Secret of the Stones

  1. They put some new ones in in the early 90s (I think), including this one at 26th & Balboa:

    I think the idea behind the bricks is that if there’s a fire or other disaster, these water supplies will be easy to find. Apparently in 1906, only the fire chief knew where they were, and he was killed in the earthquake, before the fires started.

  2. Those were great drawings and schematics that you were able to get a hold of. I had known that the bricks indicated cisterns, but have never come across such detailed drawings or plans. Very cool.

    If you would ever like any Cole Valley real estate facts or figures to use as content on your blog, just ask, I’m happy to help.


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  4. Thanks for clearing this up. I’ve always wondered what those stone circles signified but was too lazy to contact the DPW for info.

    So now the next question is how they are kept full of water (which I’m also too lazy to contact the DPW for 🙂

  5. Al

    Ha! I had thought they were markers of former streetcar turnarounds, like the ones found at the ends of cable car lines. Come to think of it, that doesn’t make a whole lot of sense…

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  7. Angela Chiu

    I never would have thought about that. A follow up investigation please! Its amazing that they still hold up considering all the earthquakes and daily traffic pressure.

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