Yes ,you need a permit to raft the dinasaur monument ,applications are taken december through feb 2. It"s a random lottery with odds of about 1in 30 for the yampa depending on the date that is applied for. The yampa is runable most years depending on weather and snow pack from aprail 10 to july 10th +or- a week ,after that the flow drops like a rock.If you want to raft the monument just to do it, the green river is raftable year round most years because it"s dam controled and late august or september permits odds are 40% to 50% draw ,class 3 and easy class 4 rapids , very beautiful 4 day trip. Down stream from Maybel and above deer park on the yampa is cross mountan canyon ,at raftable levels it is rated class 4+ to class 5 depanding in the flow, very narrow and fast , mostly done buy people with something to prove. Have fun good luck!!