Holter Lake is the most awe-inspiring of the three upper Missouri Lakes. Behind the dam lies the Gates of the Mountains, so named by Meriwether Lewis:

July 19th, 1805: This evening we entered the most remarkable clifts that we have yet seen. These clifts rise from the waters edge on either side perpendicularly to the hight of 1,200 feet. Solid rock for the distance of 53/4 miles. I entered this place and was obliged to continue my rout until sometime after dark before I found a place sufficiently large to encamp my small party; from the singular appearance of this place I called it the gates of the mountains.

The Missouri cut a deep gorge through thick deposits of limestone; although the flooding of Holter Dam (built in 1913) has decreased the rush of the river through these gates, it is still a startlingly dramatic landscape of geologic and human history. Wildlife viewing, historical vignettes, geologic curiosities, and drop-dead beautiful riverscapes make this one of Montana’s most compelling side trips.

Gates of the Mountains Inc., two miles east from the Gates of the Mountains exit off I-15 (406/458-5241, www.gatesofthemountains.com), offers guided open-air riverboat tours (Memorial Day–Sept., $11 adult, $10 senior, and $7 child) of the entire canyon. During the two-hour trip, travelers usually see bighorn sheep, mountain goats, eagles, ospreys, and deer. Guides point out Indian pictographs along the limestone cliffs. The departure schedule is complex; call or check the website for times.

Plan your day carefully, and disembark from the boat at Meriwether Picnic Area. The boat captains allow passengers to break the trip at this point. Here at the site of Lewis and Clark’s 1805 camp are trails that lead up into the Gates of the Mountains Wilderness Area, a 28,560-acre wildlife reserve within the deep limestone canyons along the east side of the Missouri River. It was back in this remote and precipitous area that 16 young firefighters died in 1949, a tragedy that led to the writing of Norman Maclean’s best-selling book Young Men and Fire.

If you lay over at the wilderness area, be certain to know when to expect a returning riverboat, and save your ticket stub.

Known simply as The Bungalow (406/235-4276 or 888/286-4250, $125–145), Charles Power’s 1911 country lodge is now one of Montana’s most historically significant bed-and-breakfasts, located near the small town of Wolf Creek in the Gates of the Mountains canyon country.

Charles Power was one of the engines of early Montana capitalism. Beginning rather humbly as a trader at Fort Benton in the 1870s, by the time of his death Powers owned 95 different corporations, controlled four square blocks of downtown Helena (including Helena’s most architecturally significant, the Power Block), and was one of the state’s richest men.

When it came time to build a country home, Power turned to Robert Reamer, the architect who designed the Old Faithful Lodge in Yellowstone Park. For furnishings, Power turned to young interior designer Marshall Fields. Many of the original furnishings remain in the stately log lodge, which offers four guest rooms (one with private bath).

There are three public campgrounds along Holter Lake, all on the east side. Turn south from I-15 at the Wolf Creek exit, cross Wolf Creek, then turn north (left) on Recreation Road and proceed a few miles to the bridge. Turn south on Bear Tooth Road after crossing the Missouri. Continue three miles to Holter Lake State Park. Four miles up the same road are Log Gulch and Departure Point State Parks.