That is very do-able! Completing all 3 in 12 hours would be a real challenge and I'm sure there would be a lot of ouch involved!!
The challenge (note that this could be done starting at TH and finishing at IC. Both ways will hurt):
IC-Start at CG loop (park at the tree access) -all CG loop, hit the access trail to the dam, all the way up to the current end at West Bottom Hollow, all the way back to your car at the CG loop.
Crowder-Start at parking lot 3 or dam lot-Ride counter clockwise-River Forks trail, Tall Oaks to NW passage, NWP to South Thompson, counter clockwise on ST to Thompson connector. TC to North Thompson. North Thompson Loop counter clockwise back to TC and back to ST loop, ST loop CCW to Steep Creek, SC to Tall Oaks, TO CCW to Parking lot 3 or Dam, depending on where you started.
Thousand Hills Trail-
(Jeff needs to write the challenge details for this section)
To keep official time and proof and also restrict participants to legal driving standards. It would be best if participants used a Garmin or other GPS unit that would track time and route. The unit would need to be fully charged and running the complete challenge period. Participants cannot drive more than 5 mph over the posted speed limit in transit between trail systems. The challenge is riding fast and long, not driving fast.
I'll be curious to see who would be up for this challenge. If you get er done, post and give the others something to compare their efforts. If you complete all 3 in a day, you are a winner regardless of your time.