What a find! This hidden gem hides behind the vineyard crested mountain range just do south of Livermore. Once you get off the 680/580 highways, you'll be immediately swept into a different wind-strewn, rocky landscape that you'll have to wind around several bends on some decent inclined well-paved roads before making your arrival to Del Valle regional park. You'll have to pay the $10 to get through, but this is one of the few parks where that fee, if maximized, is a great investment.
The campgrounds here are all incredibly well maintained, spacious (perhaps a bit too spacious and open in some places). With a great number of trails to take in any direction, the great find here is the well appointed lake that rents kayaks, paddle boats and canoes. There's even horses you can rent nearby if you get tired of all the hiking. There's plenty of places to picnic if you get tired of eating at your campsite. Be wary of the weekends, especially long holiday weekends where this park gets completely overrun. Other than this, it's a fantastic camping site. Enjoy!