The Central Savannah River Area, aka CSRA, straddles the GA/SC border near Augusta. I imagine it is the dark horse on this list–the most unexpected–despite being a Bronze-Level IMBA Ride Center. Augusta doesn’t have the scenery of the Rockies, but it does boast over 150 miles of singletrack in the area, including FATS, the only IMBA Epic in South Carolina.
The area has hosted the 2010 IMBA World Summit, and the 2011 and 2012 USA Cycling Elite, U23, and Parathlete National Championships for road racing. In 2015 and 2016, Columbia County will also be hosting the USA Cycling Marathon Mountain Bike National Championship!