I called up Crest today and the link you gave, Jim, is one year out of date. Crest is no longer under the County, it is independent now. Use this link and see current schedules.
(this is a shortcut url they've set up, the place the above gets you to is this):
Note, that the bus that goes all the way from Mammoth to Lone Pine and back is only M,W,F but daily buses go to/from Lone Pine to Bishop and different buses to from Bishop to/from Mammoth.