The cave was formed as groundwater dissolved the surrounding marble. It comprises some 3.5 miles (5.6 km) of passages and contains many beautiful stalagmites, stalactites, flowstones, cave popcorn, and other fantastic formations. The half-mile cave tour includes more than 500 stairs. On the surface above are old-growth forests of Douglas fir and cedar at higher elevations and oak, pine, and madrone forests at lower elevations; notable among the varied wildlife species are flying squirrels and the Pacific giant salamander.