FIELD GUIDE: Livingston, Montana to Columbus, Montana; Main Fork and West Fork Boulder River, Bridger Creek

Initial Publication Date: January 13, 2025

David Mogk, Professor Emeritus, Dept. Earth Sciences, Montana State University

(Download to your mobile device or print the PDF of this Field Guide (Acrobat (PDF) 4.8MB Dec31 24) for information about Beartooth Country when traveling in areas where there is no cell or wi-fi access).

From Livingston, MT to Columbus, MT (83 miles), I-90 generally follows the Yellowstone River valley.

Overview of Geologic Setting

  • Laramide faulting controls the overall topography along the Beartooth Front, and is responsible for the abrupt, high topography of the range. Archean crystalline rocks are thrust up and over the younger sedimentary carapace, forming the prominent flatirons of the Mississippian Madison Limestone that rims the range. Erosion of this uplifted crystalline core of the Beartooths have shed off the range to fill the adjacent Crazy Mountain and Bighorn Basins. Laramide faults can be viewed up close in Suce Creek south of Livingston, and in the West Boulder and Main Boulder drainages south of Big Timber. 
  • The prominent peak south of Livingston is Livingston Peak which is a slice of the Archean crystalline rocks faulted up and over the sedimentary Paleozoic rocks in the foreground, the Ordovician Bighorn Dolomite, Mississippian Madison Limestone through Pennsylvanian Amsden Formation). 
  • The foothills to the south of I-90 to the Beartooth Front traverse the southern margin of the Crazy Mountain Basin. East of Livingston, the bedrock is the Upper Cretaceous Livingston Group which contains volcaniclastic sandstones, conglomerates and mudstones. 
  • West of the West Siding exit, the bedrock is the underlying Upper Cretaceous Judith River Formation, interbedded gray sandstone and shale. 
  • To the east are large expanses of the Upper Cretaceous Sliderock Volcanic Formation, includes all the volcanic rocks erupted from the 75-78 Ma Sliderock Mountain stratovolcano (du Bray and others, 1994; Lopez, 2000). "These rocks are herein included in the Livingston Group because that terminology is well established in the literature" (Berg et al., 2000). 
  • From Big Timber to Columbus, the bedrock adjacent to the highway is dominantly the Upper Cretaceous Hell Creek Formation, thin- to thick-bedded sandstone, and gray, pale greenish gray and pale purple gray mudstones. "The Hell Creek and the upper part of the Livingston Group are laterally equivalent and are eastern and western facies respectively. Hell Creek is recognized east of the Shields River north of the Yellowstone River, and east of Springdale south of the Yellowstone River" (Berg et al., 2000). 




Interesting side trips from the main route include:

  • West Boulder River. From the NE end of Livingston, MT, take Swingley Road (S-295) south, or from I-90 take Mission Creek Road (Exit 343) south to the West Boulder River. Travel to the end of the road to the USFS West Boulder Campground.
    • Livingston Peak Trail; ~ 1 mile SE on Swingley Road turn onto Livingston Peak Road to trail head. The hike is 7.3 miles out and back and is considered to be very difficult--but well worth the views. The access road initially traverses Cretaceous sedimentary units and progresses into Paleozoic units (massive Madison Limestone); the trail to and summit area of Livingston Peak is in Archean crystalline rocks. More information and photos from All Trails or Hiiker. You may also be interested in hiking the Elephanthead Trail  (#37) whose trailhead is also in the upper part of Mission Creek and intersects North Fork Deep Creek Trail (#45) in about 5 miles; there is no developed trail to the summit, so this is a bit of a hike and scramble.
    • West Fork Boulder River Trail. This is a relatively gentle hike along the West Fork of the Boulder River, passing through the meandering West Boulder Meadows and farther south the Beaver Meadows. Connecting trails include the Grouse Creek Trail, Great Falls Creek Trail to the Main Boulder River over the Archean crystalline rocks of the West Boulder Plateau, Davis Creek Trail which connects with the South Fork Deep Creek Trail in Paradise Valley, and at the south end of the drainage going over Mill Creek Pass to the Mill Creek drainage and Paradise Valley.  More trail info from MontanaHikes.com Davis Creek Trail #38.
  • Main Boulder River.  From Big Timber, MT, take the Boulder River Road (S-298) south for up to 30 miles into the heart of the Absaroka-Beartooth Wilderness. The West Boulder Road also intersects the Boulder Road near the "town" of McLeod.  The road is paved to the Natural Bridge Falls, is fairly well-maintained USFS road to the Rainbow Creek trailhead, and a very primitive road (street vehicles NOT recommended) continues south to the Independence Mining District.
    • A popular destination is Natural Bridge Falls Picnic area and Trail, ~25 miles south of Big Timber, which includes a picnic area and handicap accessible trails. The natural bridge formed by the erosive forces of the river water carving through the Madison Limestone.  Unfortunately, the natural bridge collapsed in 1988  but the fall are still spectacular. See descriptions at: MontanaHikes.com, TripAdvisor and KMMS Radio local areas of Interest website.
    • Entering the Boulder River canyon south of McLeod, the white rock outcrops are units of the uppermost anorthosite layers of the Stillwater Complex, contiguous with those on the well-exposed Contact Mountain.
    • Numerous trails are worth exploring in the Boulder River Drainage:
      • Grouse Creek Trail (FS 14), head west 7 miles from the Main Boulder Work Station to the West Fork Boulder River Campground through Paleozoic and Mesozoic sedimentary rocks.
      • Graham Creek Trail (FS 117), traverses the lower units of the Stillwater Complex, and passes the abandoned Gish Mine, on the way up to Contact Mountain and Chrome Mountain.   
      • Great Falls Creek Trail (FS 18), also starts in the lower (ultramafic zone) part of the Stillwater Complex, traverses through the metamorphic contact aureole (orthopyroxene-cordierite or anthophyllite- cordierite hornfels, "blue" quartzite, and rare banded iron formation), and ultimately intersects Archean quartzofeldspathic gneisses on top of the West Boulder Plateau. The trail ultimately intersects the West Boulder Trail about 5 miles above the West Boulder Meadows.
      • To access the Rainbow Lakes Area, use the East Boulder River Trail (FS 27) to Rainbow Creek Trail (FS#28); total ~12 miles to Rainbow Lake or Upsidedown Creek Trali (FS 26) (~9 miles) starting at Hicks Peak Campground. The Lake Plateau area provides a great window into the 2.8 Ga granitic gneisses (equivalent to the Long Lake Magmatic Complex on the Beartooth Highway) and cross-cutting mafic dikes, and spectacular high Alpine glacial and periglacial topography.
    • Independence Mining District is one of the numerous sites of hard rock mining situated in the Eocene Absaroka Volcanics. This is a primitive road and NOT recommended for highway vehicles.
  • East Boulder River; This is the access road to the Stillwater Mining Co. East Boulder Mine, which is a major producer of Pt/Pd minerals.  Access to the mine site is restricted as mining operations are quite dangerous. 
    • Features of interest along the East Boulder River, are the Lodgepole, Enos Mountain and Susie Peak Intrusions.  These are Cretaceous igneous stocks of dioritic composition (red Kd in the geologic map). They are particularly noted for containing xenoliths of the Stillwater Complex (Brozdowski, 1985). The igneous bodies are located 8-12 kilometers north of the nearest surface exposures of the Stillwater Complex, indicating that the Stillwater Complex extends at depth at least as far north as this area. This occurrence confirms the geophysical evidence of Finn et al., (2020) that the Stillwater Complex extends in the subsurface north into the Crazy Mountain Basin
  • Bridger Creek Road (I-90 exit 384); This road traverses the foothills of the Beartooth Mountains to the Stillwater River Valley. This is a beautiful drive, but be aware that the road may be impassible in wet conditions as underlying Cretaceous shales may be very slick. Bridger Creek Road eventually intersects the Stillwater River Road, and you can head east to the town of Absarokee or west to Nye, MT and the upper Stillwater River Valley (see next section for guides to the Stillwater Complex). 

    The bedrock geology along Bridger Creek Road is mostly the Cretaceous Sliderock Mountain Formation of the Livingston Group. "This unit includes all the volcanic rocks erupted from the Sliderock stratovolcano (du Bray and others, 1994). Mostly andesite breccia (lahars) gray, pale purple gray, pale greenish gray. Andesite in clasts is porphyritic with phenocrysts of chalky plagioclase, hornblende, and pyroxene; matrix is similar but lighter in color and slightly finer grained. Very resistant, forming cliffs and very rugged topography especially near the vent zone in Sliderock Mountain area. (Lopez, 2000, Big Timber Quadrangle Map). Locally, the Hell Creek Formation crops out: "Interbedded light-brownish-gray, cliff-and ledge-forming, fine-grained, thin- to thick-bedded sandstone, and gray, pale-greenish-gray and pale-purple-gray mudstones" (Lopez, 2000)