A short distance to the north of Helena lies the Gates of the Mountains Wilderness Area which is bordered by a stretch of the Missouri lined with limestone cliffs on either side.
The name comes from Meriwether Lewis himself as the expedition again started up the river after the back-breaking portage of the Great Falls. He was certain that this was the beginning of the mountains and that they would soon cross them to find the Columbia River leading to the Pacific. He was wrong...
I took an organized two-hour boat trip down this stretch which was quite informative. We saw three bald eagles, Indian pictographs on the rocks and, most interestingly, we saw Mann Gulch which was an area where twelve elite "Smokejumper" firefighters lost their lives in a freak wild fire in 1949.
The story of those firefighters is fascinating. I suggest looking it up online.