The total title of this chapter is “Leona Heights and the Southern Oakland Hills.” This space is dominated by an necessary and strange set of rocks that share the identical deep geological story. It’s additionally an space that after had a bunch of sulfur mines, which is a very completely different sort of geological affect on Oakland historical past than these I’ve talked about earlier than.
Leona Heights was a steep little hidden valley the place the Ohlones got here often — to not collect acorns or hunt recreation, however to mine a pure deposit of ocher. This earthy stuff, consisting of varied iron oxides, is our oldest identified mineral pigment. It dates from the Stone Age cave work and doubtless earlier. California tribes are subtle customers of physique paint, and ocher is so unusual on this a part of the state that the Ohlones had a energetic commerce in it.
The Spanish missionaries had no real interest in the ocher and neither did the Mexican ranchers who took over the land, though their Indigenous ranch palms appear to have valued the location. (A small remnant is preserved at Holy Names College.) It took the Individuals to dig all of it up and switch it into home paint. Then beneath the ocher they discovered wealthy deposits of pyrite, which was as soon as important for industrial functions (it isn’t any extra).
In chapter 5 I discuss how Piedmont within the early days was a jarring mixture of chic hillside estates and noisy rock quarries. In Leona Heights too, real-estate schemes and resort inns shared this territory with sulfur mines and Oakland’s largest quarries. The title “Leona Heights” was a developer’s coinage; it was previously referred to as Laundry Farm. Inside a couple of many years after the mines closed, the realm obtained developed in numerous methods, and the indicators of the outdated days are fading however nonetheless vivid.
The rocks that contained all that pyrite are the oldest in Oakland, they usually have an extended historical past that began with volcanic eruptions below the ocean. To inform that historical past requires me to herald the fundamentals of plate tectonics, the “Earth machine” that rearranges the planet’s large-scale floor options. This three-page passage often is the steepest studying curve within the e book, nevertheless it takes the reader properly contained in the geologist’s mindset. And with that I can proceed.
Briefly, the Leona Volcanics belong to a thick slice of the Earth’s crust from the ocean flooring that was hauled onto the land and caught there, “an orphan handed off to a brand new guardian. . . . This unusual characteristic—a piece of seafloor crust marooned on land—is named an ophiolite. Having items of 1 in Oakland is a privilege.” Oakland has three separate items of this ophiolite, the second being the gabbro of San Leandro and the third our beautiful serpentinite, which I talk about in chapter 11.
None of this historical past was something we discovered about by poking round within the mines. However geologists had been doing {that a} hundred years in the past, sometimes graduate college students engaged on a thesis for Stanford or UC Berkeley. I take advantage of this chapter to introduce geologists who’ve practiced right here, what they discovered, and what sort of effort it took.
Although mining and quarrying ended way back in Leona Heights, geology continues.
The pyrite-riddled rocks are gathering new coats of ocher as floor weathering breaks the pyrite down into iron oxides, which paint the rocks crimson, and sulfuric acid, which etches the concrete gutters and paints the creeks yellow. The previous colours the current.
![Issues To Do This Weekend in L.A. [2-3-2023 to 2-5-2023]](https://www.welikela.com/wp-content/uploads/2023/02/1_FF23_FEB.jpg)
