Mostly singletrack around the lake, connects multiple trails to create perimeter trail around the lake. You can start from many points such as: Dorabella RD, Dinkey Creek Rd, Shaver Marina Etc. To complete the loop does require a bit of road riding though. You can also start just about anywhere and go out and back for a nice ride.
Mostly shaded, higher elevation, nice for a summer ride to beat the heat, but can still get quite dusty. Sometimes you might see hikers/runners or horses, but I've never had any issues. I rarely see anyone else on this trail once you're a couple of miles out of the Dorabella area.
I usually park near or on Dorabella and ride CCW. If you do you may note several different trails leaving the campground area and the residential area above it. No worries, all the trails come together very quickly and initially parallel the lake shore. The Perimeter Trail is marked to a degree with a circled "P" on trees. The link below will take you to a PDF file with a map and other information.
Shaver Lake and it's immediate surroundings are managed/controlled by Southern California Edison. They are supportive and a couple of the guys I ran into the first time out there even gave me some directions on how to connect trails, although it turned out to be pretty obvious.