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Park and Sweet Grass Counties
The Crazy Mountains rise abruptly from the plains, the result of Tertiary igneous intrusions. Magma spread horizontally between the layers of sedimentary rock, blistering the earth upward into massive, dome-like structures called laccoliths. Over millions of years, the softer rock eroded away, leaving the hard, resistant igneous rock exposed.
Visitor Access
The core of the Crazies is managed by the Forest Service and is free and open for rugged, high-alpine hiking and geology viewing. However, access is notoriously difficult due to historic checkerboard land ownership, with private ranches blocking many of the traditional trailheads. Visitors must use updated GPS mapping to ensure they stay on legal public easements.