This site is a nice hidden gem that many won't know even has a campground. While tiny and available only for a small number of campers, if you can get a spot booked well in advance, you'll have the place nearly all to yourself. Located just off of 680, you'll take Bollinger Canyon Road where you'll head just north of Las Trampas Stables before coming to a round-about where there's ample parking for about 30 cars (no worries, overflow parking on the street is allowed).
From the parking lot, there's 3-4 hiking trails to take, but the one to the campsite is the only one heading south from the parking lot. You'll have to hike all your gear in from here, and it's about 150 yards, so not all that bad, but the pathway is a bit choppy in places, so you'll want to carry most of what you've got on your back (or head!). There's just a few simple amenities at the campground, where I could only count 6-8 or so places to park a tent. Once you're all set up, take the hiking trail straight up to Las Trampas hiking ridge (there's only one trail up from your campground, so if you're not panting, then you're heading in the wrong direction). Pass the cows grazing in the meadows to climb clear to the top for a most spectacular view of Eastbay and nearby Mt. Diablo.
The other 2-3 trails that you'll find here are all worth taking and all fairly easy-to-medium in difficulty, but anyone heading up to the ridge, will find at many places it is steep and can be difficult hiking (just apply the icy hot after your hike!). As for the campground itself, it is bare minimum - the ground is relatively flat, but the entire space is encased in a barbed wire fence area playpen to keep the roaming cattle and other wildlife from coming near the area. When we were there we saw deer, cattle, raccoons and many other four legged vermin running around the area. Inside of the pen though, there's 5-6 stone picnic tables, a water fountain, only a single locker to place your food (so first-come, first served!) and a double-mounted grill.
All in all, if your aim is to spend 2-3 days scouring Las Trampas ridge, then this is a great place to call home for a few days, but it lacks the amenities and natural serenity that you would normally expect when outbacking here in Cali. And if you get tired of the campfire food, it's SO easy to just head into nearby San Ramon for a classic In-N-Out burger (it's a staple here in Cali, but I'm not from here, so I don't get what all the fuss is about: sorry California, but Johnny Rockets burgers from Chicago still win out!) or for the best bite around, try out Zachary's Chicago-style Deep Dish Pizza (this Chicagoan approves!) and a frosty cold mug of Anchor Steam to wash it down with.
Happy Camping!