As said before, there is riding along Corona Pass Road (the Road to the top of Rollins Pass), and tons of logging road off-shoots, but very little trail. The only marked mc/atv trails end after 1/2 mile. There are alot of x-country ski/mtn bike/snowmobile trails, but they are not marked as open to motorcycles.
Grand Lake/Stillwater Pass is alot better for trails, or the Willow Creek Pass area (south of Rand) is even better. Or how about the Colo State Forest north of Hwy 34 between Gould and Cameron Pass. Or Hahns Peak at Stemaboat. All of these are pretty far from WP I know, but's that all we gots.
You might want to try the St. Louis and Crooked Creeek area west of Fraser. Probably all jeep roads, but it's a nice area.
Other than that, not much up there for bikes. The Devils' Thumb Ranch and other private property has pretty much eliminated any chance for long trail riding near WP.