Try this hatch chart.
http://www.kyndoutdoors.com/fly-fish...ls.cfm?id=1769

BWO and caddis are always a good bet. Rifle is a good caddis river. Fish them in the film. Little early for hoppers and greenies but watch for them. If there are hoppers, fish one with a mysis shrimp dropper.

There is good access all through the park. There is a small parking spot and river access at the south end of the park too accessable from the road outside (you don't have to drive clear through the park to get to it).

Bob