Montana and Idaho are the two states that you want to look at.
Technically, California has the biggest wilderness in the lower 48, but Death Valley isn't anywhere I need to go.
Then you have the Frank Church in Idaho, and right North of there you have the Selway Bitterroot.
Montana has a lot of true wilderness too. The Bob Marshall Complex (The Bob, Scapegoat, and Great Bear) Then Like Mark said, we have the AB, and also the Lee Metcalf.
The Bob Marshall is where I hang out. The whole complex is somewhere around 1.5 million acres. The "backcountry" districts get hammered in their early rifle season, and game numbers are really low. But it's some of the most gorgeous country in the world, and I just enjoy being a hillbilly in the middle of nowhere.