For a really fun quick trip I would suggest taking the top off and cruising the coast highway northward. Cross the GGB, be sure to turn off of Highway 101 after the bridge crossing, drive through Stinson Beach, check out Point Reyes, get lost on some of the backroads, and enjoy the day. Also, the north coast has less traffic compared to heading south to Santa Cruz from San Francisco. The fog usually burns off by noon and the drive is relaxing. Good picture opportunities too.
Hollister is a great spot, but it would be a solid day trip, not a way go get away for "a little while". Hollister is at least an hour from downtown SF. You would want to play for 3-4 hours, then drive back. Doable, yes. It just depends on how much you like your in-laws I guess.
All of the good trails in the bay area were paved 60 years ago.
- Rollover Protip: Remember to brace yourself before you unbuckle that seat belt. You might hit your head when you fall out of the seat.
1978 CJ7 - 4.5" RE SUA, 1" BL, 35" Procomp MT, 10"x15" Wheels, 4.10 diff gears (30/20), ARB front, Detroit rear, on-board Air, 1987 258-I6 out of a YJ with a Weber Carb, XRC8 Wench