Check out Mike Reardon's Cedar Rock guide. There is at least one route in there, but it also has some beta for getting there. Consider it an adventure crag. Bring some bail 'biners a huge pair of huevos.
John Rock has several rock lines, but I've only done the most popular one. It's probably one of the better 5.9+ routes in the area. I've heard it called Rattlesnake Crack, but I don't know if that's the original name.
Park at the Fish Hatchery. Go past the gate and turn right to follow the trail along the fence line. Hike to the low spot/small flow of water and turn left without crossing it. Go to the rock face. Walk right until you see a small alcove up on the face at the base of a crack with a bolted belay. That is your line. Continue up and right (scrambling sort of) as high as possible on a dirt hill. Rack up at the top of the dirt.
Climb from the top of the dirt hill up and left in a rising traverse to the bolted belay station. 5.4ish runout.
Pull the crux right above the belay (5.9++) and climb for 180 feet of 5.7 hand crack and belay.
Move belay 20 feet left to below bolts.
Climb past bolts and to the left for another 80 feet of 5.8.