Good advice from Dhayden. If the flows are managable, the Pit and McCloud are special, and the upper Sac is beautiful too. There's some nice water right in the town of Dunsmuir.
Those rivers are notoriously tough wading and many who go there get dunked, so take a staff. There's no shame in wearing a pfd, too.
Personally, I'm too chicken to wade the Lower Sac (redding) except at a couple of places that are very tame. It's a big powerful river. The Fly Shop will indeed give you a map with spots to wade, but talk with them about safety as well...I know, I'm a coward.