Some double track but usually with people with dogs. Well marked single tracks with plenty of switchbacks and elevation changes. Reasonably difficult and fun.
Rt 395 Exit 99. Right if traveling north, left if traveling south. At 4 way intersection take a right and follow rd to stop light. Travel straight. Dam will be on your left 1 mile or so. Parking areas are scattered about the entire site.
http://www.singletracks.com/item.php?c=1&i=4869