Grand junction has some sweet trails that will most likely be drive able year 'round (Bangs canyon system, Rattlesnake). Montrose may be use able too(die trying, etc) These trails are not for stock, though... Near Denver there are a few depending on the snow load, Yankee hill, Slaughterhouse gulch... again perhaps not stock jeep trails in the snow.
Don't go alone.
But mostly in winter it is snow, and closures. Snow bashing is hard. Kicks, but work.
(some trails open late July due to snow load, July to September is it on some.)