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MONTANA–IDAHO 4x4 TRAIL GUIDE · MT-0010

Lemhi Pass

Lewis and Clark Back Country Byway · Beaverhead Mountains · Tendoy, Idaho to Grant, Montana
3/10AGF Difficulty · Easy · estimate, not driven by AGF
36 MIIdaho loop from Tendoy (BLM)
NO RVs OR TRAILERSOn Agency Creek Road (BLM); stage at Shoshone Ridge
BLM · USFSSalmon FO · Salmon-Challis and Beaverhead-Deerlodge NFs
NO BUSES, RVs OR TRAILERS ON AGENCY CREEK ROAD, AND SNOW IS POSSIBLE AT THE PASS IN ANY MONTH. BLM: "Buses, RVs, and trailers are not recommended on the Agency Creek Road." The first two miles of Agency Creek Road below the pass "are very steep and narrow with several blind corners," and BLM calls them "not appropriate" for trailers, buses and motorhomes (BLM byway brochure, 2016). Leave trailers and RVs at the BLM Shoshone Ridge Overlook on the Montana side (BLM). Expect "some steep grades, at times approaching 20%," with "a 4,000 foot gain and loss in elevation" (BLM byway brochure, 2016): use low gear, and watch for overheating on the climbs. The byway is "a single-lane gravel road with pullouts" (BLM byway brochure, 2016). Visit Montana's Lemhi Pass listing (secondary, directions from Dillon) says "The last four miles of road below the pass are quite narrow - a single driving lane," and you may have to back up for oncoming traffic. Season: "The Byway is normally free of snow from early June through October" (BLM byway brochure, 2016), but "it can snow year-round at 8,600’ elevation" (BLM byway brochure, 2016), and Visit Montana (secondary) says "It can snow at any time of the year." No source found says whether the road is plowed or maintained in winter: verify. Beaverhead County closes the Montana-side Lemhi Pass Road Dec. 1–May 15 (2026 county post; the same dates likely recur each year: verify). BLM closes all primitive roads in the Agency Creek area to motorized travel Dec. 16–Apr. 30 for big game winter range. The byway itself is exempt; side spurs off it are not. Private property: much of the land along Agency Creek is privately owned, and the byway passes a working ranch yard at about mile 30.4 with a 15 mph limit (BLM byway brochure, 2016). Stay on the road, and do not park, camp or explore on private parcels. Private ranch land may also line the Montana-side approach (Horse Prairie, near Shoshone Ridge); no official source confirms it: verify on a land-ownership map. Lemhi Pass is a National Historic Landmark (USFS; designated 1960 per Wikipedia, secondary), and about 1,329 acres around it are withdrawn from mining claims through Dec. 26, 2042 (Federal Register): do not disturb historic features, markers or artifacts. No closure for the byway was listed on the BLM Idaho, Salmon-Challis or Beaverhead-Deerlodge alerts pages as of Oct. 8, 2026, but no agency posts a live road report. Check the current MVUM and land-manager rules before you go: official closures, posted signs and private property override this guide. Call the BLM Salmon Field Office / Salmon-Challis Public Lands Center (208-756-5400) before you go, and read Know Before You Go.
AGF HAS NOT DRIVEN LEMHI PASS. THIS 3/10 IS AN ESTIMATE FROM OFFICIAL AND SECONDARY SOURCES. AGF has never driven this route (owner statement, Oct. 9, 2026), and a GPS check of AGF's 134-track archive found no track within 40 km of the pass. Everything here comes from official BLM, Forest Service, federal, state (FWP) and county sources, plus clearly labeled secondary and news sources. AGF will re-rate it after an AGF run.
WHAT THIS GUIDE COVERS

The Lewis and Clark Back Country Byway

The BLM Lewis and Clark Back Country Byway: a 36-mile loop from Tendoy, Idaho, up Warm Springs Wood Road [185] to Lemhi Pass on the Montana–Idaho line, and back down Agency Creek Road [013] (BLM byway brochure, 2016). It also covers the Montana approach from MT-324 via Shoshone Ridge, about 12 miles to the pass on road 3909 (BLM byway brochure, 2016). The Sacajawea Memorial Area is 0.2 mile south of the pass.

NOT INCLUDED: the Alkali Flat road (right fork at about mile 4.0; it "can be impassable when wet"), the Flume Creek/Ghoul Basin side tour (4WD high-clearance only; not part of the rating), Cow Creek Road, primitive side spurs in the Agency Creek area, and any private land.
WHY 3/10

Easy · Rutted, Rocky Montana Road

AGF HAS NOT DRIVEN THIS ROUTE: the 3/10 is AGF's estimate, not an AGF run. AGF rates a trail by its hardest unavoidable obstacle in normal dry conditions. It is rated to include the Montana-side Lemhi Pass Road: Visit Montana (secondary) says "We strongly advise a high-clearance vehicle on the Lemhi Pass road" and that "some sections may be deeply rutted and others very rocky," and "The last four miles of road below the pass are quite narrow - a single driving lane," where you may have to back up for oncoming traffic. The 36-mile BLM loop from Tendoy alone would rate about 2/10: BLM says "Passenger vehicles can drive the road safely but must have good tires," with grades "at times approaching 20%" and very steep, narrow sections with several blind corners on the first two miles of Agency Creek Road below the pass (BLM byway brochure, 2016). Snow, mud, wind and fire are condition changes, not part of the base rating.

Rock
2/5
Mud
1/5
Water
0/5
Exposure
2/5
Snow
4/5
Pinstriping
1/5

Snow, mud, runoff, deadfall and fire are condition changes, not part of the base rating.

ROUTE & MAP

Getting There

Idaho loop (BLM byway brochure, 2016; mileages approximate, field-verify; drivable either direction): from Tendoy on Idaho Highway 28, 19 miles south of Salmon, go 0.2 mile and turn left at the T onto the Lemhi Back Road. At mile 3.0 turn right onto Warm Springs Wood Road [185]. At mile 4.0 keep left to stay on the byway; the right fork is the Alkali Flat road. Lemhi Pass is at about mile 23.5, where Agency Creek Road [013] heads west. The Flume Creek/Ghoul Basin side tour leaves at mile 27.5 (4WD, high clearance only). Pass the ranch yard at mile 30.4 (15 mph), Agency Creek Campground at 31.5 and Cow Creek Road at 32.0. Turn right at the T onto the Lemhi Back Road at 35.6, left at 35.8, and reach Tendoy at 36.0. Montana approach (BLM byway brochure, 2016, and BLM Shoshone Ridge page): from Dillon, take I-15 south to the Clark Canyon Reservoir exit (about 19 miles, per Visit Montana, secondary), then MT-324 west across the dam and past Grant to the Shoshone Ridge Overlook / Lemhi Pass turnoff. Stage trailers there, then follow road 3909 west 12 miles to the pass. Visit Montana (secondary) calls it Forest Road 3909; whether the Montana road is county or Forest Service jurisdiction is unconfirmed: verify. The road numbers [185] and [013] are as the brochure prints them; check them against the current MVUM.

LOADING MAP…
BLM byway brochure (PDF) →BLM Idaho advisories →ROUTE FILE: not published yet

The pin marks the Lemhi Pass summit. The coordinate comes from Wikipedia (secondary); the HMdb summit marker (secondary) is about 100 m north. It falls inside the NPS National Historic Landmark boundary (converted from NPS UTM references). Official GNIS has not been confirmed: verify. It is the high point of the byway, not a trailhead. No downloadable track is published: the byway segments have not been exported or checked.

VEHICLE FIT

Rig Requirements

Stock 4x4
Yes
High clearance
Strongly advised on the Montana road (Visit Montana, secondary); passenger vehicles with good tires on the BLM loop (BLM)
Tires
Stock
Rear locker
No
Front locker
No
Winch
No
Full-size
Yes — with caution
Body damage
Low risk

Montana road: high clearance is strongly advised; Visit Montana (secondary) says "We strongly advise a high-clearance vehicle on the Lemhi Pass road" and that "some sections may be deeply rutted and others very rocky." BLM loop from Tendoy: passenger vehicles with good tires are fine (BLM: "Passenger vehicles can drive the road safely but must have good tires"). Steep grades call for careful gearing and braking. Steep grades call for careful gearing and braking. Do not take trailers, RVs or buses on Agency Creek Road (BLM); stage them at Shoshone Ridge. The Sacajawea Memorial Area cannot take RVs or trailers (Visit Montana, secondary). Carry a full-size spare, water and offline maps.

TRIP PLANNING

Know Before You Go

Season
Normally snow-free early June through October (BLM); Montana side closed Dec. 1–May 15 (Beaverhead County, 2026 post; verify yearly)
Typical trip
Half to full day; overnight option (AGF estimate)
Camping
Agency Creek Campground, room for about four campsites (BLM byway brochure, 2016); managing agency and current status: verify
Sacajawea Memorial Area
Day use only (Visit Montana, secondary); official rules: verify
Trailers
Not recommended on Agency Creek Road; stage at BLM Shoshone Ridge
Turnaround
Pullouts and parking areas; single-lane sections
  • Hunting season: Montana's general deer and elk season runs Oct. 24–Nov. 29, 2026 (FWP). Expect hunters, camps and parked vehicles; wear blaze orange outside the vehicle. Archery season runs to Oct. 18. A youth deer hunt runs Oct. 15–16 (FWP). Agency Creek Campground "is always full during the fall big game season" (BLM byway brochure, 2016). Idaho-side seasons were not researched: check Idaho Fish and Game.
  • Fire: the Salmon-Challis Stage 1 fire restrictions order #0413-00-04 (Idaho side) runs through Oct. 31, 2026 unless rescinded; it was not listed on the forest alerts page on Oct. 8, 2026: verify. Beaverhead County Stage 1 restrictions on private land (Resolution 2026-28, Aug. 10, 2026, "until further notice") showed no rescission: verify. Check before any campfire.
  • Bear country (Montana side): Beaverhead-Deerlodge food storage order 02-00-22-02 applies Mar. 1–Dec. 1; the order runs through Dec. 31, 2026 or until rescinded. Idaho-side food storage rules were not researched: verify.
  • No garbage service and no cell coverage at the Sacajawea Memorial Area (Visit Montana, secondary). Pack out everything.
  • Thunderstorms "with lightning, strong winds, and rain or hail are likely in the summer months" (Visit Montana, secondary).
  • The 2020 Bear Creek Fire had burned about 10,700 acres in the Lemhi Pass area as of Aug. 24, 2020, and closed Lemhi Pass Road from MT-324 to the pass at the time (KXLF, news, historical). Watch for falling snags in old burn areas (AGF advice).
  • Contacts: BLM Salmon Field Office / Salmon-Challis Public Lands Center (208) 756-5400; Salmon-Challis Leadore Ranger District (208) 768-2500; Beaverhead-Deerlodge NF, Dillon (406) 683-3900; BLM Dillon Field Office, Shoshone Ridge (406) 683-8000. The BLM byway web page lists 208-373-4000, which is the BLM Idaho State Office, not Salmon.
SOURCES

Sources & Review

Last reviewed Oct. 9, 2026, from agency pages checked Oct. 8. No byway closure is listed, but RVs and trailers are not recommended on Agency Creek Road, the Montana side closed Dec. 1–May 15 in 2025–26 (Beaverhead County; 2026–27 dates: verify), and snow is possible in any month. AGF has not driven Lemhi Pass; the 3/10 is an estimate from official and secondary sources, counting the Montana-side road.

AGF ratings describe normal, dry-condition difficulty. They do not mean a route is legal, open or passable today. Spot something out of date? Use the Contact page.