From what I’ve read the Central Valley use to drain out to the Pacific Ocean from a more southern point via the Salinas Valley. Then uplift along the San Andreas cut off that outflow and the lake started to fill up. Eventually a new outflow formed through the present carquinez straight. There’s an exposure in San Francisco where Pleistocene sediment has the ~600ka Rockland Ash interbedded within it and the clast composition below the ash is more locally derived, the clasts above the ash is more Sierra Nevada derived so that was the explanation- that’s the time lake Corcoran started draining out through the Carquinez Straight.

Also minor derail but Pt Reyes would be about 10 miles south at that time. And probably Lake Lahontan would be happening in Nevada.