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 the satellite view of the same area shows how much of it is forest, which also fascinates me.
Most of this land is inaccessible. There’s 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 rules of river names say that the name of a stream applies to the most vigorous branch, and if the stream splits into branches of the same vigor the name can be arbitrarily assigned to one branch, or none. Thus the upstream end of Sausal Creek is where Shepard Creek and Palo Seco Creek join. So on this map I’m extending Lion Creek up its northernmost branch (although it may well be that by this criterion Horseshoe Creek should be Lion Creek). 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 Mine on it. Because the mine site is so important, I’m giving that particular stream the name 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.
By early last year, the mine site had been fixed up so it looked clean.
And down below the mine the stream looked pretty good.
But as of a couple weeks ago, 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 are dissolved in drainage water besides iron, which are more toxic. I don’t have any chemical data from the water, so I can’t address the true hazard. But this stuff is harmful in other ways, specifically 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 encasing the whole hillside in concrete. And we won’t do that.
Oakland Geology 