2,800 acres, all beautiful. The center of activities is a creek running through a redwood grove, but there are miles of trails, canyons to descend into, and hills to huff-n-puff up.
The campsites look nice - car camping, no environmental sites - but I have never been able to get a reservation. Looks like you need to call well in advance (ie, six months may not be enough time).
Potable water is available.
From Highway 101, take Sir Francis Drake Boulevard past the town of Lagunitas. Continue for a couple of miles and look for signs.
USGS 7.5' Topo Maps