Boulder River


Big Timber, MT
United States United States
45.85274, -109.92374
65 Miles

The Boulder River originates in the rugged, high elevations of the Beartooth Mountains in the Gallatin National Forest. It tumbles down 7,300 feet and 60 miles through mixed conifers, deciduous trees, shrubs, grassland, and agricultural land, to join the Yellowstone River. Total length is 65 miles long.

The river is a popular destination for fly fishing. Other attractions in the valley include several church camps, a guest ranch, and several USFS campgrounds. The Forest Service also maintains several guard stations, trailheads, and picnic areas in the valley.

From where the Boulder River begins, at the confluence of South Fork Boulder River and Basin Creek, the river runs through a narrow and small valley, flanked on all sides by the towering Absaroka Mountains and the Absaroka-Beartooth Wilderness Area. For the first thirty miles, the Boulder River predominantly runs through public land, with a few scattered parcels of private land lying about. Access is excellent - just pull off the side of the road and go.

This upper section of the Boulder River has very fast current, lots of whitewater of Class III and Class IV, excellent pools and solitude for the angler willing to walk away from areas where the road nears the river. While it is rather time consuming and a slow drive to access this section, the upper Boulder River is well worth the trip.

Thirty miles downstream from its origin, the Boulder River flows through Natural Bridge Monument, a unique waterfall that is well worth taking the time to see. As the Boulder River flows through the monument, the river disappears entirely in a large mass or rocks, re-appearing one hundred feet later in two distinct waterfalls that cascade down more than one hundred feet. The sight of water flowing out of the rocks, not just over it, is a unique site, and well worth the price of the short walk required to see it.

Below Natural Bridge, the Boulder River passes primarily through private land as it leaves the Absaroka Mountains behind and begins to flow through the high plains. The valley just outside of the mountains has extensive agricultural operations. Fields of hay go right up to the rivers edge.

The current of the Boulder River also slows. The country becomes much more open, offering excellent views of the surrounding mountains.

After flowing for more than thirty miles below Natural Bridge, the Boulder River reaches the confluence with the Yellowstone River near the town of Big Timber, MT.

Game Fish Opportunities:

Brook Trout, Brown Trout, Mountain Whitefish, Rainbow Trout, Yellowstone Cutthroat Trout


The Boulder River lives up to its name on the upper stretch with boulders of every size everywhere. And they are slick, even in good wading shoes. Combine that with a very fast current and some deep pools. Heavily forested and bushy banks. Undercut banks in the lower river.


Fishing from the bank often isn't an option as the bank is just too heavily forested and bushy for most of its length.

Below Natural Bridge State Monument, the size of the fish greatly increases. Rainbow trout and brown trout predominate, with fish stretching up to twenty-four inches occasionally taken.

Fishing on the lower stretch is excellent for dry fly fisherman and streamer fisherman alike. Using large streamers in the many deep holes and along the undercut banks is a wonderful way to catch the rivers large brown trout. For the dry fly angler, the Boulder River has excellent caddisfly hatches throughout the summer. Due to the relatively low fishing pressure, standard dry flies like the Parachute Adams and Elk Hair Caddis work very well.

Spot Access:
Parking (car/truck), Picnic Area, Shore fishing access, Camping, Fly Fishing, Wading, Floating
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Map for 45.85274, -109.92374
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Trout, Brook (Salvelinus fontinalis)


Trout, Brown (Salmo trutta)


Trout, Cutthroat (Oncorhynchus clarki)


Trout, Steelhead (Rainbow) (Oncorhynchus mykiss)


Whitefish, Mountain (Prosopium williamsoni)




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