A brief visit to Mills College for the recent pow wow reminded me of some business — not unfinished business, but rather an inquiry ready to renew. The upper end of the Mills grounds is very different from the lush central campus with its beautiful floodplain setting, and it has the possibilities of bedrock and fault-related findings. And it’s been seven years. To refresh our memories, here’s the geologic map.
Pine Top is labeled Jb next to Lake Aliso at the east end of Mills College. Qpaf, Pleistocene alluvium (the Fan); Qhaf, modern alluvium; Jsv, Leona volcanics (Jurassic); Jb, basalt; Jgb, gabbro
I’ve always wondered about Pine Top. It stands up so steeply and dramatically at the foot of the high hills, right on the Hayward fault (which is poorly localized here). The digital elevation model of the hill makes it look as if it had been quarried, and indeed there are records of a quarry on the college land.
I’ve also wondered about Pine Top because the basalt “Jb” is hard to find, and I came up empty on my first visit. The hill appeared to be fully mantled in soil.
The campus is especially pretty right now. I hope they can get past their problems and resume their long successful history in Oakland.
Lake Aliso is its usual self, thanks to the late-season rains.
Supposedly the lake is a sag basin related to the Hayward fault, but I’m starting to think that it owes its existence entirely to damming.
This old photo of the lake, from around 1893, shows the side of Pine Top nicely forested in oaks, which would not be the case had there been a quarry there. I think the quarry was located north of the lake where the freeway now runs.
This time I found the original footpath up the hill. Students used to have costumed processions up this path, bearing torches and regalia.
At the top, they would assemble around the Hearth and enjoy their celebrations.
Maybe some alumnae with long memories can add comments about how it used to be.
The view from the top has closed in as the trees have grown, but in the old days it was surely fine.
But anyway, this time I found bedrock — well, pieces of it, around the big microwave tower that was emplaced up here since my last visit. Here they are arranged for a portrait. I also found a little in the old footpath.
This is not basalt by any means, not even a highly altered basalt. This is the highly altered ash of the Leona volcanics, what the old-time geologists with their eyeballs and hand lenses called the Leona Rhyolite. That calls into question not only the “Jb” label for Pine Top, but the whole stripe of Jb drawn on the geologic map. Just some more things to go and check out this summer.
Oakland Geology 
14 May 2022 at 2:45 am
“Nestled among the Eucalyptus trees, lies a Mills hearth designed by Walter Ratcliff, J., up on Pine Top Trail near Lake Aliso and used to be emblematic of Mills College.” –
http://www.thecampanil.com/Uniquecampusodditiesexplained/
25 April 2022 at 7:22 pm
If you challenge the “Jb,” are you, as it were, launching an assault on entrenched theory, or is Oakland geology a more fluid expertise ready to be tweaked where needed?
25 April 2022 at 9:03 am
The original name of the Mills College riding academy was Lake Aliso stables. The Cress family bought the business in 1928; it became Cressmont – the winning entry in a contest to choose a new name for the equestrian program.
Prior to the construction of the MacArthur Freeway, Calaveras Avenue extended to the stable site, under today’s Mills corp yard.
The pathway to Pine Top that Andrew describes was part of the Upson Downs cross-country riding course.
Andy Dietz, co-owner of the Pot-Pourri gift shop during its decades at the Lincoln Square shopping center, recalled nocturnal mounted forays to Mills for skinny-dipping in Lake Aliso.
(Pot-pourri has a new location in Berkeley, on Vine Street.)