Spanning a distance of 40 miles (64 km), the Crazy Mountains are located between the Musselshell and Yellowstone rivers.

The Big Timber Stock, a large igneous intrusion, forms the bedrock in the Crazy Mountains.

[1] The stock is of Tertiary age, and consists of diorite and gabbro with zones of Quartz Monzodiorite, which has been intruded by many dikes and sills.

In 1916, the Crazy Mountains were proposed as a location for a national park, yet Congress failed to pass the legislation.

"[2] The Crazies are almost completely surrounded by private lands making access into the mountains somewhat difficult, especially in the southern section where the highest peaks are located.