The grove at the parking lot.
In fact, I did not see anyone else on the trails. I took the Laurel Loop trail to the Lower Sea Foam trail to the Upper Sea Foam trail, but there are a number of different options to get there. There are free maps available at the trailheads, but they don't cover the section of the hike outside of the park.
On the way up. That's San Pablo dam and reservoir.
At the highest point of the Upper Sea Foam Trail the trail makes a sharp turn. At this point head away from the trail, and cross the fence. When I was there (2/2017), there was a gap with only one strand of barbed wire, next to the gate. There is a fire road on the other side, down a bit. Follow the road to the left, and it will head downhill until it breaks out of the trees and starts climbing. The peak is easy to see once you're out of the woods.
If you come to another fence, turn left up the hill to the summit. If you cross the fence then you will have gone too far. The summit has some flat areas to set up, with the fence running across it. There is a USGS benchmark at the summit, so its easy to figure out if you're at the correct point.
The summit benchmark.
I set up, and the rain started to pick up. I brought a sheet of tyvek for some shelter. The wind kept it plastered to my back, and it worked until rain started pooling in the bottom. I kept the radios in a plastic bag to keep them dry. My log however, got damp. I made 10 contacts on 30 and 20 meters, including one in NH. By this point I was wet and getting cold so I didn't try VHF. I packed up, and hiked down in the rain and mud. By the time I got back to the parking lot, the rain had mostly stopped.
So much mud (and water).
Overall it was a nice hike, and the summit seemed like it would be pleasant to operate from in nicer weather. This weekend of activations, though, made me realize my wet-weather SOTA setup is totally inadequate. This might not be a problem, since California is so sunny, but being more prepared is good in general.
Trailhead: Kennedy Grove Regional Recreation Area off of San Pablo Dam Road. Parking free November - March, a few dollars rest of the year.
Website: Sota Page. Park site: http://www.ebparks.org/parks/kennedy
Maps: KB1KXL SOTA Hikes map
Route: Get to the high point of the Upper Sea Foam Trail. Head away from the trail into the woods, cross the fence, and follow the fire road on the other side left (generally North at this point). Very muddy and slippery in/after rain.
Red Tape: It is unclear what land the summit is on, but it is not in the Kennedy Grove park.