I've never fished it this time of year but I absolutely LOVE fishing Rock Creek just east of Missoula. Until recently I made an annual trip there at the end of June. At that time of year we had our best luck with stone and salmon fly nymphs above a san juan worm. For drys we would use stone and salmon flys then fall back to a variety of smaller flys. Rock Creek is paralleled by a small dirt road and while there can be a number of people fishing it it really feels like a wilderness trip. My favorite spots are from the Bitterroot Flats upstream. There is a fly shop at the begining of the dirt road and while a little eccentric they have always been very helpful with info esp. if you buy something. There are many, many, many big fish in this creek and I think it is well managed. I'll post a pic when I get a chance.
George and Michael Estey a couple miles up from Bitterroot Flats on Rock Creek, Montana