I like to brag that Oakland contains more rock types within its boundaries than any other city in America. But alas, it’s missing one of America’s most widespread rock types: limestone. Yes, there are pods of dolomite limestone in the Claremont Shale, but that’s a far cry from what Oakland’s first outside settlers hankered for, which was real calcite limestone.
Limestone is essential for civilization because it’s the default industrial source of lime (calcium oxide or hydroxide), without which you can’t manufacture any kind of decent mortar, or plaster, or cement. Lime has been made for thousands of years by simply roasting limestone, which consists of the mineral calcite (calcium carbonate). This was traditionally done in a lime kiln, a stone furnace that was loaded with rock and firewood.
The Bay area does have bodies of limestone, and these were staked out early. But the nearby firewood supplies (i.e. forests) were soon depleted, and the industry was fitful and limited until reliable supplies of coal and, still later, oil became available.
One alternative to limestone in Oakland was oyster shells, which we once had in abundance. Unfortunately, many of the old Native shellmounds had oyster shells in abundance too, and this led to the end of them.
A few years ago I had the chance to visit the remains of an old-fashioned lime kiln in the Santa Cruz Mountains.
Another old site was on the coast near Rockaway Beach, south of Pacifica. I wrote a piece about it for KQED a while back that explains where most of our local limestone comes from, tectonically speaking.
This kind of industry lasted only a few decades. Around the turn of the last century, big manufacturers started to mine massive bodies of limestone. One was on the Santa Cruz County coast at Davenport; it supported a company town out there for a whole century. Another was in the South Bay near Cupertino, based in a quarry on Permanente Creek. One of Henry J. Kaiser’s early companies operated it, and when Kaiser eventually became head of an industrial giant, during World War II he took the name Permanente for the name of his innovative company health-care plan. The quarry is still digging, almost 80 years later.
Another big limestone quarry was in American Canyon, in Napa County. But the one that fascinates me most is the former Cowell lime quarry, which sits between Walnut Creek and Concord, on Lime Ridge. For about 40 years, starting in 1908, this quarry exploited a thick deposit of travertine — hot-spring limestone. It supported a company town too. Now some of the workings are in Lime Ridge Open Space, where you can scrutinize these unusual deposits. They aren’t like anything else around.
This post was inspired by my maniac brother Steve, who explores the woods around his Lyme, New Hampshire home to locate old cellar holes. Now he’s branched into old lime kilns.
In other news, I’m happy to report that the latest Covid-19 guidelines now allow the use of public transit for outdoor recreation. This means that all of my geology walks and rambles can be undertaken again, and I’m looking forward to getting out there, taking due care of course.
Oakland Geology 
1 June 2020 at 12:25 pm
The hill above Cowell was also mined for gypsum, which occurred scattered through the claystone. Unfortunately, the bedding of the rock in that hill is flat but not level. Water entering the loosely filled pits at the top of the hill lubricate the bedding planes, and that hill slides towards the Cowell and Turtle Creek subdivisions, taking Ygnacio Valley Road with it.
The City of Concord a while back cut the part upslope of Ygnacio Valley Road, so continuing movement would only disrupt fenced-off open space. But they haven’t really finished the road repair or stabilized the landslide.