[2] The Stephen Mather Wilderness provides a protected area for a wide variety of wildlife, including elk, mule deer, gray wolf, mountain goat, moose, and bighorn sheep.

Species of wolverine, bat, duck, hawk, owl, frog, loon, chipmunk, coyote, squirrel, bear, falcon and eagle are also fairly common.

[3] There are approximately twenty-eight species and subspecies of fish found in the wilderness, including the threatened bull trout and anadromous runs of coastal cutthroat trout, Dolly Varden, steelhead, and five species of salmon found in the Skagit, Nooksack, and Chilliwack drainages.

[3] Common recreational activities in the Stephen Mather Wilderness include backpacking, camping, wildlife watching, climbing, and hunting.

Much of the area can only be reached by multiday hikes, often combined with mountaineering, through remote, trailless territory.