>>1142804in colorado volunteer departments probably do both, either due to urban-wildland interface or from going on wildland striketeams. and regardless, experience is experience, and connections are connections. if you live in district of one i'd say go check it out. go during business hours and introduce yourself and find out when they train (probably weekly), show up to a couple drills to observe and see if it's still something you'd like to do. bring ice cream the first time if you really want to make a good impression.
if you want to skip that and go straight to seasonal wildland firefighting, look for wildland academies (i don't know about co, but in ca you can find 67 hour academies that get you a bunch of wildland certs), firefighter 1, fire tech associates degree, emt, wilderness first responder, and find online when the hiring process starts for usfs, national parks, and state fds.