Oakland Geology

Leona Heights was very different from today at the turn of the last century, though it was still called by that name. “Leona Heights” was a real-estate project that extended into the secluded grassy valley long known as Laundry Farm. It used the familiar gambit of building a streetcar line into a large landholding and selling home lots there, with the promise of easy suburban living among other white folks, quick transit to jobs, and fast profits for lot flippers. But Leona Heights was even more different, because the streetcar line was a pre-existing freight line that served Laundry Farm’s mines and quarries, including the big Leona Heights Quarry.

Today Leona Heights still fits the suburban ideal (minus the whites-only exclusion), but many of those cozy homes rest on piles of mine and quarry waste. And the thickly wooded hills above them hide traces of those industrial times to this day. The old quarry grounds are still a gravelly wasteland north of the college campus. Recently I’ve been poking around up there, guided by the modern-day miracle of lidar-based digital elevation models that strip the vegetation from the bare ground. They promise truth―some day―but at the moment they add confusion.

Here’s an example. I’ve been exploring the woods northwest of Merritt College in the territory centered around the top of the Horseshoe Canyon tramway. It’s mostly dense chaparral or overgrown oak forest full of poison oak. An ordinary aerial view shows almost nothing useful.

A map assembled by Steven Mix in 1999 (find it on the Oakwiki) shows a lot of former mine and quarry sites in the same area. The tramway top is shown as the “concrete bunker” in the center.

And yet the lidar image, acquired since Mix compiled his map, shows major differences.

It’s up to somebody to resolve them. Probably not me, certainly not at the moment, but I can report bits from the ground, fragments of truth.

I’ve concentrated on the big gash in the ground west of the old pit. It really stands out in the lidar image but isn’t recorded in any document, so the mystery line seemed like an easy target:

A detailed site map from 1898 shows the tramway structure and a rock crusher that sat next to it, and the road now called the McDonell Trail to its north, but no trace of the mystery trench. That’s one constraint. The other constraint is that the tram line heading west-southwest burned to the ground and was abandoned in 1913. So my working theory is that the mystery trench held a railway built after 1913 that served both the upper quarry pit and the Crusher Quarry below via a new tramline, aimed due west, that reached the concrete catenary ramp preserved today north of Belfast Avenue. Here’s how it all looks to me.

There appear to be no trails to the eastern leg of the trench. I had to scramble cross-country to reach and leave it, cutting my way through underbrush and creeping along deer trails. And the prevalence of dead tree branches that snap off with a light touch, like the cobwebs in a horror film, is a sign that people don’t ever come here.

The trench is as deep as 4 meters, partly due to dirt piled up along the sides. I saw no sign of any hardware in the trench, like rails or ties.

The lower portion of the trench is more accessible. It’s apparent as a set of depressions on the steep slope that end at the very top of the Crusher Quarry scar. Again, there’s no hardware left behind. It’s picturesque.

The trench has potential! I think the upper portion could be cleared out and turned into a proper trail through a nice bit of woods.

The lower portion is too steep to develop. People are making their way through there anyway, including mountain bikers. The traffic will degrade the slope, as it has elsewhere in this area. But I like being there anyway.

Maybe some of the old-timers in the audience can tell us more about this trench.

This entry was posted on 10 June 2024 at 8:01 am and is filed under Quarries and mines. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.