Just outside of Zion National park is Gooseberry Mesa, a classic table-top mesa with a trail around the rim. Absolutely a classic mountain bike ride and well worth seeking out. Similar to getting to Zion NP, the best bet is to fly into St. George and rent a car, which is what we did (this trip was combined with canyoneering, a separate post). For real hammerheads, I guess you could fly into Hurricane and ride the 20 miles to get to the trailhead.
West Coast Flying Adventures 