The Missouri River Canyon and Old US Highway 91

The Missouri River Canyon and Old US Highway 91. . The Lewis and Clark Expedition passed through this canyon of "nearly perpendicular rocks" during its journey up the Missouri River in July 1805. Although the men grumbled about mosquitos and prickly pear cactus, the Corps of Discovery was clearly impressed by the Adel Mountain Volcanics, the eroded remains of a pile of volcanic rocks that flank the river for forty miles. The volcanic rocks you see next to the Interstate consist mostly of fragments from violent, explosive eruptions that occurred about 75 million years ago and continued for several million years. , Although the arrival of the Montana Central Railroad in 1887 did much to open this region to settlement, it was not until the early 1930s that a modern paved highway provided a direct connection between Helena and Great Falls through this area. U.S. Highway 91 wound its way along the Missouri River through the volcanic outcrops of the canyon, crossing the river over two large steel truss bridges that still carry traffic in the vicinity of Hardy and Wolf Creek. The Hardy Bridge is visible on the old highway below you. Though bypassed by Interstate 15 in the 1960s, today old U.S. 91 provides motorists a unique opportunity to experience a Great Depression era road through one of the most spectacular landscapes in Montana.