Two weekends ago we camped for a night at the top of Mt. Diablo. We took a pretty incredible summit hike and got to enjoy a spectacular sunset, but besides that the actual campsite was pretty mediocre. I recommend going up there for a hike and a picnic. It you aren't camping there is a $10 vehicle fee and you have to leave before sunset because they close the gates. I am still enjoying the freedom of being able to pick and go. And it's always nice to get some elevation and the new perspective that comes with it.