We had these rocks pretty buffed out in the early-mid '90s and they saw a lot of traffic. Pretty much every possible line and variation was climbed. Jim Hansen used to take the PUC rock climbing class out there to practice and it was he that placed the welded bolts/chains. I found the angwish boulders and a couple of us dug them out of the jungle and scrubbed them. That didn't last long though. If you dig around in the moss you'll find a bolt on top to help with cleaning. There are a number of other bouldering spots in the area near Linda Falls, and Devil's Punchbowl, and the short cliff that Floyd references, but Mossy Rock is probably the best.
Chris, send me a private e-mail if you're interested in checking out several decent lead climbs, both trad and sport, on a 35-45 foot crag in Angwin. By the way, the Angwish Boulders suck--not worth cleaning!
Kudos to Pacific Union College for allowing the public free access to this site. I usually work out on the rock a few times a week (yep, that's me in the photo). More detailed directions and a topo are posted on my website at:
My ratings differ a bit from Chris's (mine are usually more conservative). If you get the chance to climb there, I'd appreciate feedback on the ratings. Later this summer I hope to do some major cleaning on the moss-clad Angwish Boulders, another 15 minutes beyond Mossy Rock.