Lakeside Park has undergone a lot of changes since Edson Adams put Oakland’s first golf course there. For one thing — and the thing behind this post — over the year the city has brought in rocks to a place that originally had none at all. Some of them are boulders that hold plaques: I won’t be talking about those. This is about the other ones, the working rocks who have the basic job of standing in your way, like the guard rocks down at Middle Harbor Park.
I take a walk around the lake every week, but this last week I took a few extra ones to visit all the working boulders. I think there are three generations of them. Here’s a selection.
The main road through Lakeside Park appears to have the first generation. My working theory is that the city parks department tapped a stash of rocks that were acquired on its own properties, principally Joaquin Miller and Leona Heights Parks. That accounts for the following mix of rock types. The majority belong to the Leona volcanics, probably sourced from Leona Heights Park. They present many different textures with an underlying lithology of light-colored, strongly altered volcaniclastic material that takes on an orange iron-oxide glaze with exposure. These five specimens illustrate the range of this rock unit.
The other boulders include nondescript ones I can’t confidently identify. Behind the rear lawn-bowling field is this laid-back hunk of what sure looks like Sierran granite.
But there’s a specimen of serpentinite, worth a close look, next to the Nature Center.
And right in front is the lake’s special star: this wild, glittering piece of blueschist.
Another generation of boulders sits along the path in front of Children’s Fairyland. It too consists of local stones: besides the Leona volcanics it includes proper sandstone belonging to, if I’m not mistaken, the Oakland Conglomerate in Joaquin Miller Park.
Near the entrance is a splendid serpentinite boulder.
And best of all are some good specimens of the ocher-bearing material from the Leona volcanics that the Ohlone tribes once prized.
The third generation of stones is of recent vintage, installed during the park’s bond-funded upgrade. Their main hangout is on the shore east of the boathouse by the parking lot.
Another grouping is in the brand-new Snow Park extension at the foot of 20th Street.
When these went in I thought they were sandstone (and said so here), but upon closer inspection I conclude that they’re some sort of welded tuff, not from anywhere in the Bay area, probably some place across the Central Valley or the desert beyond. That’s OK — Oakland welcomes immigrants. The material is fairly featureless, but these rare clasts look like bits of country rock that got torn off and taken up during the eruptive cataclysm that made this stone.
The lake shore also has plenty of cut and dressed stone, in the form of benches and curbs and capstones. They’re all commercial quarry granite, hardworking stuff that will last forever, but without the personality of real live boulders.
Oakland Geology 
11 March 2020 at 10:06 am
Dude awesome! I knew you might be the only person I could imagine who might know this! Thanks for solving the mystery.
10 March 2020 at 4:35 pm
I think they’re the same sandstone blocks found farther up Lakeshore past the commercial district, which were recycled from the original Oakland High School and originated in Indiana.
10 March 2020 at 3:54 pm
I know it’s not your main thing, but there are bunch of striking old marble or granite cut pieces that border the children’s swing sets by the library at Lakeshore Park. If you go over there and look, they seem to be from the rubble of some old grand building or temple or cathedral.