Don't know if there are any serious mountain bikers here, but there are 2 events coming up worth mentioning.
Sept 27: "Revenge of the Rattlesnake" MTB race. Coinciding with the leaf peepers festival. It's gonna start at Timberline this year and end in Davis. Designed to beat you down it will run a course approximately 36 miles or so through some of the gnarliest trails possible.
Oct 4th: "Tour de Lilly" Tour/fun ride led by the owner of blackwater bikes, roger lilly, followed by a BBQ and maybe even lunch will be brought to a stop somewhere along the way.
Both are not really for the faint of heart tho! Might want to test yourself by riding something like Plantation Trail first to see its something you might find "fun"