The Rainbow Trail is 100 miles long and located in the Sangre de Cristo Mtns south of Salida. About half of it is single-track trail; the rest is ATV trail (south end). The northwest end of the trail is at Silver Cr; the southeast end of the trail is near Medano Pass. Trails Illustrated map #138 'Sangre de Cristo Mountains' and the San Isabel National Forest visitor map show the trail and adjacent access routes, communities, campgrounds and other points of interest. Both are printed on plastic paper, and I like the TI map best.
You can access the far west end of the trail at Silver Cr (near the Kismuth Mine) or jump on the trail south of Salida (you'll miss the first 15 miles of trail) - Map of RBT near Salida Note that the very west end of the Rainbow Tr is non-motorized (open to bicycles, horseback, and hiking only). This is the section west of the Kismuth Mine. The trailhead for motorized access is east of the mine about 1/4 mile and is easy to spot because there are signs and a sign-in stand.
More Rainbow Tr pictures GPX and mileage info A short ride (youtube, watch at 720pHD)
Ride reports on ADVrider:
Bergs Over the Rainbow 2012
/\ Camping Trip: Rainbow Trail, Sand Dunes & Back 2014
Somewhere over the Rainbow 2010
Rainbow trail update 2015
Click pictures to supersize.