Over the years I’ve done a lot of poking around Leona Heights, the large hill looming over the south end of the Warren Freeway. You’d think I have a nice photo after all this time, but instead here’s a vertical view from Google Maps, terrain view. It shows the area between Horseshoe Creek, at the top, and the former Leona Quarry at the lower right.
The hillside is deeply eroded by several steep gullies, all of which still have running water in them at this time of year. Those fascinate me. And much of it is forest, which also fascinates me. Most of the land is inaccessible. There are only two fire roads, few trails, and very steep slopes well guarded by brush and poison oak. Apparently the city owns much of it.
And here’s the stream map to help with the creek names, because they’re confusing. Each of the Leona Heights gullies is interesting, and I’ll be showing them to you in coming weeks, but this week I’ll focus on the one labeled Leona Creek.
The streams in these hills all feed Lion Creek, originally named Arroyo del Leon. The name of a stream applies to the most vigorous branch, by convention, and if the stream splits into branches of the same vigor the name can be arbitrarily assigned. So on this map I’m extending Lion Creek up its northernmost branch. People also talk about “Leona Creek,” sometimes applying the name to all of Lion Creek and sometimes applying it to the nameless creek that has the former Leona Heights Mine on it. Because the mine site is so important, that’s the one I’ve labeled Leona Creek.
This creek once had potential. It has a nice catchment, seen here from the Merritt College parking lot toward the north end of Ridgemont Avenue. The woods are impenetrable.
But then the creek reaches the old mine. This was in 2016.
By early that year, the mine site had been fixed up so it looked clean.
And down below the mine the stream looked pretty good.
But by mid-2017, it was back to its old trick: acid mine drainage.
What we’re looking at is yellow and orange iron oxides, precipitated out of the acidic water as it’s neutralized. They aren’t poisonous in themselves, and the water won’t eat the flesh off your fingers. But other metals dissolved in it are more toxic. Without chemical data from the water, you can’t tell the true hazard. But even so this stuff — yellowboy — is harmful by blanketing the streambed so that living things can’t live on and in the gravel like they’re used to: insects and insect larvae, which feed other insects and birds and so on.
Acid drainage is natural in the Leona Heights, to a certain degree. The rocks hold a lot of pyrite, which oxidizes to yield sulfuric acid, so there’s always a little acid around. The mine, however, opened up the richest part of the hill and gave it access to oxygen.
The raw chemistry of pyrite oxidation is not that fast. But sulfur-oxidizing bacteria make their living by eating pyrite and pissing out acid, and the old mine is like a giant party condo for them. They won’t stop for anything short of us sealing up the whole hillside, an expensive challenge.
UPDATE: It looked like this in late 2018.
The officials who monitor this creek are pleased with the progress, but vigilant. Read the comments for more detail.
Oakland Geology 
31 July 2017 at 8:38 am
John C. and I were up there while they were doing the work. It looked like a million bucks, expense not beauty. So was the work successful? Did they at least greatly reduce the acidity downstream? I look forward to more posts on this area.
31 July 2017 at 11:43 am
What was being mined?
31 July 2017 at 12:52 pm
Pyrite, or marcasite to some, for making, big surprise, sulfuric acid. Most of it went to Stouffer Chemicals in Richmond.
31 July 2017 at 5:34 pm
I always heard that the sulfur was more of a seam sometimes ‘mixed’ with lead and zinc (galena & sphalerite).
BTW, my theory is that the laundry farm was located at/near the bottom of the creek for precisely this reason, sort of a poor mans bleach.
28 August 2017 at 9:43 am
I love living in the Bay Area where so many people are interested in our fascinating mining history and geology. I wanted to point you towards some information you might not be aware of on the project at http://www.waterboards.ca.gov/sanfranciscobay/water_issues/hot_topics/Leona.shtml.
My name is Lindsay Whalin. I’m the case manager and a geologist/inorganic geochemist at the SF Bay Regional Water Quality Control Board. We are the agency that required and oversaw this remediation work.
You might be interested to know that the highest priority in cleaning up this mine was isolating the piles of mining waste from rainfall and runoff, because they were a huge source of sulfuric acid to Leona Creek when it rained, leading to extremely high concentrations of metals. We measured the creek pH as low as 1.5 (that is between battery acid and lemon juice) and concentrations of Pb at 100x, and Cu and Hg at 10,000x levels considered protective of aquatic habitats, but only during the rainy season.
We’ve been overseeing monitoring of the creek since completion of the project that suggests this effort was successful, with concentrations of metals and metalloids below ecotoxicity standards. The now stabilized slopes are revegetating nicely with native species. We’ve observed damsel-flies in the water, lots of evidence the site is being used by wildlife including as a critical corridor through the woods, and moss growing on the creek bed. So, we are actually thrilled with progress so far.
It is understandably disappointing that the creek bed still turns orange from iron-oxidation, but that wasn’t the focus of this cleanup effort. We will continue to monitor the creek, and will require additional work if needed, but so far the 1 seep on site that we know is impacted by mining activities continues to improve (latest pH measurement was 5.8). There are 2 other seeps that are contributing to acidity in the creek likely via acid rock drainage, however we do not have evidence that these are caused by mining activities (as you are aware there are low pH seeps throughout the hills in this area due to pyrite). We cannot require cleanup if the phenomenon is natural; only if the impacts are caused by humans.
I’m sure the property owner would like me to remind you that it not public property. Access is restricted both for your safety and, as you can imagine, it’s critical that those slopes remain stable. Please feel free to contact me to discuss this and other mine sites in the Bay Area. My contact info is included on that webpage.
10 March 2023 at 1:57 pm
I’ve tried to contact Lindsay for an update to her previous very helpful comment, but she has moved on to another state environmental agency. I welcome word from the stream monitors, especially during this exceptionally wet winter. — Andrew
10 March 2023 at 5:24 pm
Per our Regional Board website the current contact for mine investigation/cleanup is Keith.Roberson@waterboards.ca.gov (510) 622-2404. Since RB2’s main remediation case closed in 2015, there might be more involvement in review of ongoing monitoring by contacts at CDFW and ACE, shown at Lindsay’s presentation https://www.waterboards.ca.gov/sanfranciscobay/water_issues/hot_topics/Leona/10_Leona_CAOamdntTSO_4_website_B.pdf