The Missouri River Canyon and Old US Highway 91

The river below the overlook is not the one Lewis saw. His Missouri held one trout, the westslope cutthroat; the fish here now are mostly rainbows and browns, wild and spawning in the river, fed by the steady, clear water released from Holter Dam upstream. Anton Holter and Samuel Hauser began the dam as the Wolf Creek Project in 1908, and it was finished in 1918. The thirty-five miles from the dam to Cascade became one of the West's best-known trout tailwaters, and a 2017 state survey counted more than 170,000 angler days a year there.

What the plaque says

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 mosquitoes 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.

Where it stands

Worth the stop nearby

• Mann Gulch — 19 mi
  Thirteen markers on a grass slope above the Missouri, where a fire outran a crew of smokejumpers in 1949.
• Fort Shaw Indian School — 24 mi
  An Army post turned boarding school, whose Native girls went to the 1904 World's Fair as an exhibit and came home champions.

More markers nearby

• A Volcanic Island in the Rocky Mountains — steps away
• Michael John MacKinnon — 4.4 mi
• "Cliffs High and Steep" — 4.4 mi
• The Mann Gulch Fire — 13 mi