Rocks of the Bilger Quarry

It’s been twelve years since I wrote about the former quarry where the Rockridge Shopping Center sits today. Except for the pond, the whole space has gotten a makeover and it’s time for a fresh look. But first, some nostalgia. Back in 2008 the 24-hour “Big Long’s” was still there. I used to shop there; it had everything.

And flanking it was the big old Safeway with more businesses between and beyond, and the bank in the far corner. I used to bank there.

All of this is now gone, and the site is under intermittent redevelopment. Decades ago this was a giant rock pit, active for more than 70 years, that for a long time was the largest rock quarry in Alameda County. It was started by the Oakland Paving Company in 1870, and the name of Frank Bilger was associated with the succession of enterprises that produced crushed rock here, so it’s usually referred to as the Bilger Quarry. (Bilger learned the trade from his father, a German immigrant, and he surely pronounced his name the German way with a hard G.)

Now the Long’s site is a big Safeway, and the old Safeway and bank buildings are part of an empty lot. Only the water-filled pit on the east side is unchanged, and the walls show no sign of decay, which is a very good thing because it’s right next to St. Mary Cemetery.

The whole quarry site occupies a small body of quartz diorite, an intrusive (meaning it didn’t erupt) igneous rock that’s unusual but not unheard-of for the Franciscan Complex. It’s mapped as the purplish blob in the center labeled “Kfgm.”

It happens to be excellent rock for industrial and engineering purposes. The Tribune in 1890 wrote, “The material used by the Oakland Paving Company is a crushed blue rock, a trap dyke that is practically indestructible, submitting without injury to the hardest usage for eight or ten years without repairs, and with proper care, such as any pavement requires, lasting three or four times longer.”

The east end of the quarry exposes the bluish stuff. This exposure, right behind the Safeway, also has flaky veins of calcite. It’s very tough — not that I’ve used a hammer on it lately, but after seeing lots of rock you get a feel for this.

The west side consists of a much lighter material, a bit coarser grained and slightly less durable.

Between them is a contact zone that I recall as being black and sheared, with mineralization that was probably iron-manganese oxides. It was covered up when the new Safeway went in and parts of the rock face were fixed up for safety. I took this photo in 2018 from the roof parking lot.

There’s chainlink netting on the rock face, just in case it decides to start crumbling onto the roadway.

You’re always cautious about building inside an abandoned quarry, because rocks don’t last forever — that’s why they’re mostly underground, covered with soil. The experts have assured us it’s OK, and I trust them pretty well. The cemetery will last a good long while, and the former California College of the Arts campus, while it looks precarious perched above the other side, has passed muster too and someday will be apartments with good views.

What continues to impress me, every time I visit, is how different Oakland used to be. Throughout the late 1800s, the cemetery on one side and the CCA site (then it was the Treadwell estate) on the other were cheek-by-jowl with this huge operation that blasted three times a day, starting at six in the morning, and employed hundreds of men in producing crushed rock. But back then, rocks were money.

5 Responses to “Rocks of the Bilger Quarry”

  1. Steve Hanson Says:

    I am a native of Oakland and studied some geology when i went to Merritt College, so always enjoy your articles. I put myself thought school by working as a lifeguard for OPR and then later on subsequently working for the Port of Oakland for many years. I have always wondered about the history of that quarry- thanks for the info. I also know that many people have somehow gotten into the area and drowned over the years- there is really no way out. What is that metal latter structure? I used a picture of the quarry one time when I put together a program (after some tragic drownings in the Oakland estuary) where a troop of ex lifeguards went to every elementary school to teach kids about water safety and what to stay away from. It certainly is a good example of a water hazard. By the way, I also loved that Longs. Local ownership makes a difference.

  2. oaklandrocks Says:

    Was so nice to receive your blog post – for some reason, I have been missing them for the past year. That is an interesting area and yes, I too shopped at the Longs. Seemed to be the go to place for last minute school projects – Mom I need poster board NOW!!!! Question, it the blue rock similar to what Upper Rockridge sits on? I always heard that it sat on some sort of blue rock but I sell real estate and we hear all sorts of stories…some true some not.

  3. Amelia Sue Marshall Says:

    The workers at the Bilger Quarry included immigrants from Italy. Giancarlo, historian for the Fratelanza Club, told me that it was good work for men who came to the USA without English language proficiency. They went on to build many of the brick and stone structures in older neighborhoods. Skilled stone masons from Lake Como and Liguria built the stone structures in Tilden and Alvarado Parks with the WPA.

    The city deserves credit for requiring the developers of the retail center to put in the nice outdoor seating area with informational displays about the history of the Bilger Quarry.

    For those who oppose development of the CCA site for more luxury condos (with good views) – NO affordable units, increasing displacement and homelessness – you are invited to join me in writing to city officials to urge them to use their power of eminent domain. They could save the CCA rock ridge for an arts campus and build their condo towers in the vacant acreage at 51st and Broadway.

    Apparently the developers ran out of money to replace the acreage where the Chase Bank and Safeway used to stand, and there is a land restriction on the title saying that it can only be used for retail. Retail is diminished in the current economy, and AFFORDABLE housing is needed. EMINENT DOMAIN!

  4. Andrew Alden Says:

    “Blue rock” was the common term in the local stone industry for dark, hard sandstone and related rocks. Telegraph Hill, in San Francisco, was made of it. The large quarries in present-day Piedmont all produced “blue rock.” The fresh rock has a slight bluish tint from the presence of low-temperature metamorphic minerals, primarily pumpellyite. But the name was applied to all sorts of rock, like here. It’s like “granite” countertops, most of which aren’t true geologist’s granite.

  5. Mary Wood Says:

    Very cool

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