Situated in the southwestern section of the US state of Montana, the Boulder Mountains are a north-south oriented range of 69 named mountains, the highest and most prominent of which is Haystack Mountain (8,812ft/2,686m). The Boulder Mountains are located between two of Montana’s major cities, Helena and Butte, and are contained within Deer Lodge, Jefferson, Lewis and Clark, and Silver Bow Counties.
The mountains are a subsection of the greater Central Montana Rocky Mountains and are more or less cut off from nearby ranges, due to the network of interstate and state highways that surround them. In fact, I-15 cuts through the middle of the Boulder Mountains, separating the southerly Haystack, Bear, and Sullivan Mountains (among others) from the northern part of the range, which includes Pole, Jack, and Thunderbolt Mountains. The Boulder Mountains are bordered to the northeast by the Elkhorn Mountains, to the northwest by the Lewis Range, to the west by the Idaho-Bitterroot Rocky Mountains, and the southeast by the Tobacco Root Mountains.
Geologically, the Boulder Mountains share a fairly common history with the Elkhorn Mountains. Both are part of the Boulder Batholith that is located between Butte and Helena in the region between the Deer Lodge Valley of the Upper Clark Fork River and the Broadwater Valley of the Upper Missouri River.
The batholith was created 73 to 78 million years ago during the Late Cretaceous era when a period of high volcanic and tectonic activity created massive magma intrusions in the region. Subsequent subduction between two smaller tectonic plates in the region that’s now Montana and Idaho helped bring the magma toward the surface of the Earth’s crust. Then, uplift throughout the region pushed the resulting granite further up to the surface, where they were eventually exposed to form the mountains we see today.
The region of the Boulder Batholith and, subsequently, that of the Boulder and Elkhorn Mountains is incredibly rich in precious metals, such as gold, silver, copper, lead, and zinc, which was part of the impetus behind the Montana Gold Rush in the 19th and 20th centuries.
Although they are not the highest mountains in Montana, the Continental Divide does travel through part of the Boulder Mountains. Indeed, a small section of the Continental Divide Trail even meanders its way through the range.
Most of the Boulder Mountains are located within the Beaverhead-Deerlodge National Forest, particularly within the Deerlodge subsection. The Deerlodge National Forest covers an area of 1,227,155 acres and straddles both sides of the Continental Divide in the Boulder Mountain Region.
The region of the Boulder Mountains is the ancestral home of the Blackfeet, Salish (Flathead), Shoshone nations, among others, who lived off of the plentiful big game in the area. Within the mountains, one can find plenty of moose, bighorn sheep, brown bear, Canadian lynx, and other charismatic megafauna. Ponderosa pine, spruce, fir, and juniper trees cover the forests in the Boulder Mountains while the lowlands are awash with various sagebrushes, grasses, and even cacti.
These days, much of the Boulder Mountains remain remote and relatively inaccessible. While some trails crisscross the region, off-trail travel and a sense of adventure are a requirement for trips into the Boulder Mountains.
There aren’t many maintained trails within the Boulder Mountains, so if you’re looking for an adventure, just grab a map and head out into the backcountry. But, if you are looking for a trail, you have a few options:
One of the United States’ three main long-distance hiking trails, the Continental Divide Trail is a rugged path that crosses some of the most stunning scenery in the country. The trail enters Montana at Raynolds Pass and continues on for 400 miles until it reaches its northern terminus at the US/Canadian border.
The Continental Divide Trail meanders its way around the city of Butte before turning in and heading up through the Boulder Mountains. Starting off at the Homestake Pass Trailhead, just outside of Butte, you can follow the trail straight into the Boulder Mountains for a bit of an adventure.
If you want to bag the tallest peak in the Boulder Mountains, this short trail up to the summit of Haystack Mountain is your go-to. This trail starts off of Forest Road 1538, which is just a short drive off of I-15 near Butte, Montana.
From the trailhead, hikers can walk from the Forest Service Gate for 4.8 miles to the summit of Haystack Mountain and take in the views of the surrounding landscape. Although it might not be a long trail, the path to Haystack Mountain is steep, so you really have to earn the vistas at the end!
Planning an adventure to the Boulder Mountains? Here are the closest cities and towns to the range:
The fifth-largest city in Montana, Butte is home to over 33,000 people. Located just south of the Boulder Mountains, Butte is a good place to start your trip in the range if you’re traveling from another city to the west along I-90. the town has an assortment of different lodging and dining options for visitors, too!
The city of Helena is the capital of the state of Montana. Although it’s the state’s sixth-largest city, Helena is home to nearly 30,000 people and has a bustling downtown area. It is the economic center of the region and is located just east of the range along I-15.
Situated to the southeast of the Boulder Mountains, the town of Bozeman, Montana is an outdoor enthusiast’s paradise. While it might be a few hour’s drive from the Boulder Mountains, Bozeman is one of the larger cities in the state and is even home to a fairly busy airport that gets flights from a variety of major cities around the western United States.