The Plan:
Drive up Angles Crest Highway and meet at the base of the lift. We will ride as long as you want but no later than 4PM. Bring your lunch and plenty of fluids.

Cost: Mountain Bike Tickets All Day - $25

Logistics: I don't think cell coverage works up there so make sure you are on time. If you are later - no problem. Bring your radio and tune in 7 07. The mountain is pretty small so we are bound to bump into each other.

UPDATED - Mountain Bike Trails:
Lynn's Flume Ride
Mt.Waterman Access Road
Mt.Waterman Trail
Buck Horn Trail
"Any way per Cody's description and the actual owners of
MT waterman who we are speaking with on a thread started on STR
there are clean smooth trail(s) that go back to the lifts"
I read that as "beginner". I think there is something in it for everybody.

Driving Directions:
You will need a USFS Adventure Pass - $5. There is a place to buy them @ the intersection of Angeles Crest and Forest Highways.
From the intersection of I-210 and Angeles Crest Highway (SR 2), drive north on Angeles Crest Highway 9.5 miles to Angeles Forest Highway. Keep straight.
Continue about 4.5 miles to the junction with the Mount Wilson Road at the Red Box Ranger Station. Keep straight.
Continue 19.8 miles farther on Angeles Crest Highway to a parking area on the left, just past the Mt. Waterman ski lift. Park here. There is a restroom just below the road at Buckhorn Ranger Station.