On the grounds of Holy Names College is a locality where the locals, before the Spanish moved in, would find and process the red mineral pigment of hematite.
Today it’s the setting of a toddlers’ playground, without a sign of its former prestige. Nearby is Oakland historical landmark 51, the George McCrea House and Indian Campground. McCrea was the prominent architect who designed the house, and I find nothing online about the Indians. I don’t know if these boulders are part of the historical landmark, but they aren’t being treated like one.
I visited the site a couple weeks ago accompanied by a rockhound and a geologist. The boulders have numerous pits, much like the ubiquitous mortars where the natives once ground acorns.
The material making up the boulders appears to be ancient colluvium cemented by abundant iron oxides. This cementation would not happen at the land surface. They sit on a shoulder of land near a deep ravine of the Lion Creek drainage, evidently exposed by erosion.
The site is not far from the former sulfur mine in the hills above Laundry Canyon, and I was told that other ironstone boulders occur in the neighborhood.
Hematite is an excellent orange-red stain, useful for face paint and similar decoration. There isn’t much around here.