The Mullan Road was carved into the face of the mountains high above the Clark Fork River west of here after Lieutenant John Mullan tried to keep his wagon road as close to the river as possible but was forced to seek an alternate route when a mountain spur reached all the way to the river’s edge. Mullan later wrote that making the six-mile cut through rocky spurs was an undertaking he almost feared to attempt. On May 10, 1860, he assembled his entire work force of 150 citizens and soldiers at the west side of the spur, and for the next six weeks his men dug, whittled, and blasted their way up the mountainside to an altitude of a thousand feet above the river. A premature explosion while clearing a path through the rocks wounded one man and severely stunned another. When completed in June 1860, the Big Side Cut segment was the most awe-inspiring of the entire 624-mile Mullan Road, and in 1862 a traveler called it a narrow wagon track that left no room for careless or uncertain driving.