I did a backpack/fly fish trip to the 1000 Lakes Wilderness off of Highway 89 by Hat Creek last year. We took the road to the trail head and hiked about an hour and a half (3 miles or so) and camped at Eiler lake. We went in mid August and the water was low but there were plenty of rainbows in the 12-16" range. There are several other lakes in the area that are an easy hike from an Eiler base camp. Try a hike from Eiler to Everett, I didn't get to fish it last year but reports said that it had nice fish that were eager to take a dry fly. I fished #16 parachute adams and some bigger attractor flies, #10 yellow humpy) and caught a decent number of fish on all of them. One word of caution: The mosquitos can be pretty bad so take repellent. I would also take one of those fin mesh mosquito nets you can put over your head. Have fun!
http://www.google.com/products?hl=en&q=mosquito+net+hat&sourceid=navclient-ff&rlz=1B3WZPB_enUS357US357&um=1&ie=UTF-8&ei=zLJES-WJDIG6NZSt_NgG&sa=X&oi=product_result_group&ct=title&resnum=1&ved=0CCAQrQQwAA
For more info you can check out the following links:
http://www...;WID=599&tab=General
http://www...pack/places/thousand.htm
Trev