I missed seeing this by a few days, but you passed right by what used to be Skaggs Island (off CA-37, just east of Sonoma Raceway). It used to be a Naval comms site and my dad worked there through his retirement in 1991. I remember going to a Halloween party in 1989 or so, in costume as Mark McGuire, of the two Bash Brothers. We lived a few places in the Bay Area back then...in Morgan Hill, south of the bay, and then in Fairfield, which OP probably passed through from the central valley.

Thanks for the memories, OP!