Oakland Geology

Maple Avenue, in the upper Dimond neighborhood, used to be called Quarry Street. It was an old county road that served at least two quarries, starting with the Fruit Vale White Cement Gravel quarry in the 1870s. The road entered a small valley that cut through the southern tail of the Piedmont crustal block and over a small saddle in the ridgetop to the quarry, which exploited the light-colored fault gouge along the Hayward fault. Here it is on the digital elevation map based on a lidar survey of the fault zone a few years back.

This post is about the second quarry, which has had various names over the years. Its old scar is in the center of the image.

It was opened by James O’Brien some time before 1883 and was known as the O’Brien quarry. Later, when John F. Curran took it over, it became the Curran quarry, but it was also called the Fruitvale Red Gravel quarry, probably to differentiate it from the nearby white gravel quarry. Curran, a Canadian-born resident who died in 1912 aged 72, owned land around present-day Curran Avenue.

Like nearly all Oakland quarries, it produced crushed rock. Some jobs, like roadbeds for trains and cars, demanded hard “blue rock,” but there was also a good market for crummier stuff, and that’s what was here. Being so near the fault, the rock was pervasively shattered, which left it open to weathering and alteration. The area is mapped as mixed Franciscan rocks, which doesn’t tell us much because “Franciscan” is a grab-bag term.

^{Qpoaf is really old gravel, KJf is undivided Franciscan rocks, and Jsv is Leona volcanics. Find it on the main geologic map toward the middle.}

In 1904, the county was asked to give Quarry Street the more appealing name of Maple Avenue. (At that time Oakland had not yet annexed it.) Later that year the owner of the 22-acre parcel the quarry sat on offered the “Crescent View Tract” to the county for use as a hospital, but nothing came of it. The state mineralogist took note of the Curran Quarry in 1906: “The rock is termed ‘red cement gravel,’ and is a very much altered rock, recemented by a red clay. Used as a top dressing for roads and walks.”

The area got annexed in 1909 and developed by the 1920s, but the quarry pit was abandoned at an unknown date and sat vacant until after World War II. It’s visible at the top of this photo from the winter of 1945, at which time the city owned it.

^{Original photo from Oakwiki}

The pit was subdivided and filled with homes over the following decade, and today it looks like anywhere else up there.

The house on the corner has a wonderful exposure of serpentinite that deserves its own post some time.

From the street, everything looks green and lush and fine. From across the valley, though, there are spots visible where that “red cement gravel” has been freshly exposed by our recent hard rains.

Quarry pits are wounds to the land that Earth tries to heal.

I devote a chapter of my upcoming book to Leona Heights, where I review the human history of this much-disturbed area and introduce the geologic history of the much-disturbed rocks.

There were three waves of digging in these hills. The Ohlones started it thousands of years ago, harvesting ocher for a thriving regional trade. In 1891, Fritz Boehmer resumed ocher mining in earnest to supply his paint factory. Then the Realty Syndicate, trying to make a few bucks from its vast land holdings, opened a rock quarry where Merritt College sits today. That was in 1896.

Finally Boehmer, whose ocher operation had ended when his factory burned down, found amazing deposits of pyrite ore next to Redwood Road and got into the pyrite business in 1900, opening a mine that he named after his daughter. The Alma Mine produced ore for the next 21 years, one of several pyrite mines in these hills.

Records of those mines are scant and confusing; some appear to have changed names with new owners, and all the shafts and adits (well, almost all) have been sealed. But I’m pretty sure about the Alma Mine: where it was and what it left behind.

Supposedly the first tunnel was dug near Fritz Boehmer’s roadhouse on Redwood Road, which appears to have been where the Lincoln Square Shopping Center sits today. I’m going to show a bunch of maps now. The shopping center’s next to the Warren Freeway, route 13, at the upper left corner of the next two images, a 2006 aerial photo and a blend of the digital elevation model with streets half-superimposed.

The 1915 topo map shows Redwood Road as it used to be, with a symbol where the mine was. It’s where the gas station is today, or under Terrabella Way.

An old-timer told the Oakland Tribune in 1950 that “friction set fire to the ore about 1908. The shaft was blocked off and the company moved operations further around Redwood Road, digging another tunnel to hit the same deposit at right angles.” Plagued by repeated fires from pyrite dust and the mining collapse that followed World War I, the Alma Mine ceased business in 1921.

The next edition of the topo map was issued in 1947, after Redwood Road had been rebuilt, and there was no sign of the mine, or any other structure, from the earlier map.

But aerial photos from the intervening years show what happened. This image from 1939 shows the old course of Redwood Road and the wasteland of tailings left below the first mine site. The second mine entrance was to the east, at the point of the sharp bend in the road. There appears to have been an ore transport line going from there straight southwest down to the old train tracks that used to run beside Lion Creek.

A year later, the area was being rebuilt as a Key Line streetcar route was pushed up Redwood Road, driving residential development past the upper Laurel toward the future Crestmont neighborhood.

This 1947 airphoto shows the new configuration of Redwood Road along with the ghost of the old road. The former mine pit was being mitigated and the new road exposed a lot of fresh rock; at the same time, land was being cleared along the big curve for new structures. (A ground-level photo from 1949 shows the rugged walls of the old pit.)

The 1958 topo map, with updates to 1980 in purple, shows how thoroughly the area was transformed after that.

Which brings us to today. Here’s a closeup of the 2006 imagery with the locations of the following photos I took last week.

The pavement entering Terrabella Way is deeply eroded by acid runoff from the exposed rocks, which are still full of pyrite.

And the iron oxides left behind continue to form fresh ocher.

The 1940s roadcut below Terrabella Place is strongly colored by iron oxides. It’s why this area was rich enough to support a mine.

It will take a long time for vegetation to cover the scene of the old mine.

The pit is really rather deep here. Now it holds the Redwood Reservoir, a big steel tank. I could definitely come back and spend an hour with these rocks.

And then there’s down below, on Geranium Place, where the old mine tailings plus the road construction have left bad ground. That caught my eye a few years ago, and it’s just as bad as ever.

When it comes to mines, especially pyrite mines, the past is never really past.

It’s a bit frustrating reaching the limits of the available information. There are surely other records out there I could consult, but not during a pandemic.