Off Hwy. 15, about 12 miles north of Helena, Montana
Some 300 million years in the making, Meriwether Canyon, through which the Missouri flows, is spectacular to see. Limestone cliffs, intricately folded and studded with fossil remains from the ancient Mississippian sea, rise sheer above the river to 1,200 feet.
The "singular appearance" stunned Meriwether Lewis on the passage through here in 1805; it appeared the river had ended, until Lewis noted in his journal that the rocks opened up like "the Gateway to the Rocky Mountains."
The site can only be accessed by trail or boat. Cruises of the nearly six miles of gorge are available from Gates of the Mountains Landing. From the boat you can see ancient Native American pictographs and perhaps bighorn sheep, goats, and bald eagles. The boat stops at the Lewis and Clark campsite before its return run, where you can enjoy time off the boat swimming or bird-watching.
Boat tours June–Sept. Fare charged.