Backbone Rock is a geological wonder — a 50-foot-thick fin of ancient rock through which the U.S. Forest Service has carved what is said to be the world's shortest tunnel, allowing Beaverdam Creek Road to pass directly through the mountain. Surrounding the rock formation is a beautiful recreation area with swimming holes, picnic facilities, a campground, and hiking trails through old-growth hemlock forest. The area is one of the most visited natural attractions in Johnson County and a beloved summer swimming destination. Spring wildflowers and fall color make it equally spectacular in those seasons.