June | 2022 | Oakland Geology

Archive for June, 2022

Signs of the old Alma Mine

20 June 2022

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.

Posted in Quarries and mines | 4 Comments »

A closer look at Haddon Hill

6 June 2022

My book manuscript (now in the copyeditor’s hands) has a chapter about the Fan, our peculiar region of gravel hills that stretches from Pill Hill to Evergreen Cemetery. In the book I refer to it as Oakland’s second level. I briefly recount its human history, starting with the trouble it caused the initial Spanish exploring expeditions (led by Fages in 1770 and 1772 and by Anza in 1776), then go on:

“Today, whether we drive, ride or walk across the second level, we can still see the underlying landscape and picture how it looked to our predecessors. The eastern, uphill side of the Fan, toward the Hayward Fault, is a string of hills of the third level, most of which are bedrock. The downhill side, toward the Bay, is a variegated landscape of low rises and small gaps through which the Bay sparkles and distant mountains across the water loom, in detail or in silhouette as the weather changes.”

What drives this passage is the bit about picturing how things looked to our predecessors. That might sound romantic — and it surely is — but it’s also a basic skill of geologists, especially in the urban setting.

I sometimes think that as I look around at the Fan, I’m craving glimpses of the hills as they appeared to the Ohlones during the thousands of years they were managed as meadows, the way they appeared in the 1850s when the Town was founded. The Ohlones kept the hills clean to support their lifestyle. Today we keep the hills populated and planted in trees to support our lifestyle. Before humans lived in this country at all, during the ice ages and the warm breaks between them, these hills were either oak-bay woods or cold savannah depending on the climate. The best time for geologists was during the Ohlone years, when the Fan was laid bare.

There are no images from that time. We can only imagine how it looked and felt. To illustrate the tools I use, let’s take Haddon Hill, in the heart of the Fan next to Lake Merritt, as an example (specifically, it’s the Haddon segment of Lobe 4).

First there’s the Bache map from 1857. Although it was primarily a navigation map, it showed details of the surrounding land as well, including Haddon Hill.

The physiography isn’t very precise, but the shoreline and roads can be considered reliable.

Second is the digital elevation map (available in the National Map viewer), which strips the buildings and vegetation off the land.

The composite map, made using the transparency slider, is less stark and easier to deal with.

Haddon Hill is a triangular area defined by the lake, the freeway and Park Boulevard. It has two easy avenues through it that go up little valleys, the northern one on Wesley Avenue and the southern one on Athol Avenue. All the other roads tend to be straight and ruthless. If you walk or bicycle here a lot, you know this already.

When Oakland was a tiny town huddled at the foot of Broadway, Haddon Hill had a road running south through it, undoubtedly based on an Ohlone path, that climbed up from Indian Gulch where Wesley tops out, worked along the 100-foot contour and eased over the hill where Haddon Road meets Brooklyn Avenue, then went down into the southern valley where Athol runs today. (The path branching off to the east along the hill’s crest is probably the route Anza took in 1776.) That all changed when the settlers moved in and cars took over everything. Today gravity doesn’t matter as much, and when we read Friar Juan Crespi’s account of traversing the hills here, “which, although they are all treeless and grass-covered, annoyed us very much with their ascents and descents,” maybe we don’t feel it like he did in 1772.

The old road came down Athol from the right in this view north from the intersection of Athol and Newton Avenues.

Finally we get to the geology part.

^{Qpaf, Pleistocene alluvium (the Fan); Qmt, Pleistocene marine terrace; af, artificial fill}

The “Qmt” part is the same marine terrace that runs through Clinton, and I have to say I disagree with the map. I think the terrace extends only to the “P” in “playground.”

Whenever I venture into the Fan, I’m beguiled by the neighborhoods but always look past the homes and landscaping for the wider views. Here are a few examples from 21st-century Haddon Hill. They tend to come in glimpses. This glimpse from across Park Boulevard, at 9th Avenue and E. 28th Street, shows the St. Vartan church, conveniently on Haddon Hill’s highest point, and Grizzly Peak.

This view down Booker Street shows the lower part of Haddon Hill hiding Lake Merritt in front of downtown. Brooklyn Avenue is just visible in front of the Ordway Building.