From 1859 to 1860, the Mullan Road was constructed from Fort Benton, then part of Dakota Territory, to Fort Walla Walla, Washington Territory. The Mullan Road bypassed Tower Rock and its canyon: The Mullan Road only followed the Missouri River until it reached the Dearborn River. Rather than enter the Missouri River canyon, it struck inland and passed south through a wide, flat prairie about west of the river. This allowed the road to skirt the rugged Adel Mountains Volcanic Field. The Mullan Road then followed the valley of Little Prickly Pear Creek back to the Missouri River near present-day Wolf Creek, Montana. North of Helena, the road left the Missouri and followed Tenmile Creek and Austin Creek up to Mullan Pass, where it crossed the Continental Divide. In 1866, the Little Prickly Pear Wagon Road Company secured a license to manage the Mullan Road from Craig to Helena, and made significant improvements to it.