I've only been to the Boise area once and that was last July. Fishing on the South Fork of the Boise was great but watre levels are high that time of year. WOuld likely be even higher during June.

I HIGHLY recommend Angler's Fly Shop in Boise. The folks there were GREAT. The owner, John was awesome and one of the young guys there actually drew us a river map that was incredibly accurate. It came in really handy as we floated the river. Their service to us was outstanding even though we were not hiring a guide.

http://www.boiseanglers.com/boiseanglers/Anglers.html