South O'Brien Loop
South O'Brien Loop is a 8.6 miles trail in Lolo National Forest, Montana. The Forest Service rates it trail class 3, developed. It is open to hiking, horse and pack stock and mountain biking.
Trail conditions, closures and hazards are not tracked here. The Lolo National Forest official page carries current alerts and closure orders.
Map
One end Other endLine simplified to about 100 metres. Basemap from the USGS National Map.
| One end | 46.8529, -114.1676 · Directions ↗ |
| Other end | 46.8529, -114.1678 · Directions ↗ |
The ends are the two ends of the longest connected chain of segments. The record does not say which is the usual start.
The trail
| Length | 8.6 miles |
| Trail class | 3, developed |
| Type | land trail |
| Surface | native material |
| Typical grade | 10-12 percent |
| Typical tread width | 18-24 inches |
| Motor vehicles | Closed to all motorized use year-round |
| Accessibility | Not evaluated |
| National designation | National Recreation Trail or other national designation |
| Trail numbers | 123 |
| Forest | Lolo National Forest (unit 0116) |
| States | Montana |
| Detail published | management level, with uses |
Values are the set across all segments. Class 1 is minimally developed and class 5 is fully developed. Grade and width are the forest's typical values, not measured extremes.
Allowed uses
| Hiking | Allowed 01/01 to 12/31 (month/day) |
| Horse and pack stock | Allowed year-round |
| Mountain biking | Allowed 01/01 to 12/31 (month/day) |
A use is listed when the Forest Service records it as managed, accepted or discouraged on any segment. Discouraged still means legal. Uses marked restricted are left out. Where the forest publishes a Motor Vehicle Use Map, that map governs motorized use.
Trailheads
The Forest Service recreation layer records no trailhead within a third of a mile of this trail's line. Many trails start from a road pullout or another trail with no trailhead record. The forest's recreation pages list the trailheads it does publish.
Distance is from the point to the nearest part of the trail line. Season text is what the forest wrote and is often a season name rather than a date. The recreation page link goes to the Forest Service site, which may redirect to the forest's recreation index.
Camping nearby
No federal campground is recorded within five miles of the trail. Dispersed camping is allowed on most National Forest land outside posted closures. The forest office has the current rules.
Campsite Atlas cards carry site counts and booking links from Recreation.gov. Forest Service cards come from the recreation layer and link the agency page.
Fire nearby
- PrescribedBison Range Br2F Rx
35 mi from the trail midpoint
- WildfireNorth Fork Lost Horse
48 mi from the trail midpoint · 118 acres · 70% contained
- WildfireMoose Mountain
48 mi from the trail midpoint · 5,832 acres · 90% contained
- WildfireBlack Bear
50 mi from the trail midpoint · 2,126 acres · 30% contained
Distance is to the reported incident point, not the fire edge. Closure orders are on the forest's official page.
Explore
Reference
Questions people ask
How long is the South O'Brien Loop?
8.6 miles, the sum of the 1 segment the Forest Service records under this name in Lolo National Forest.
Source: Forest Service trail layer
What is allowed on the South O'Brien Loop?
hiking, horse and pack stock and mountain biking. The trail is closed to motor vehicles year-round. Some uses are seasonal. The allowed uses section lists the dates.
Source: Forest Service trail layer
Where does the South O'Brien Loop start?
The line begins at 46.8529, -114.1676 and ends at 46.8529, -114.1678. No Forest Service trailhead is recorded within a third of a mile of it. The record does not say which end is the usual start.
Source: Forest Service trail layer
Is the South O'Brien Loop in a wilderness area?
No. The trail line does not cross any polygon in the National Wilderness Preservation System layer.
Source: Wilderness Connect
Where can I camp near the South O'Brien Loop?
No federal campground is recorded within five miles of the trail. Dispersed camping is allowed on most National Forest land outside posted closures. The forest office has the current rules.
How developed is the South O'Brien Loop?
Trail class 3, which the Forest Service describes as developed. Class 1 is a minimal, unimproved route and class 5 is fully developed, often paved.
Source: Forest Service trail layer
How steep and how wide is the South O'Brien Loop?
The typical grade is 10-12 percent. The typical tread is 18-24 inches wide.
Source: Forest Service trail layer
Is the South O'Brien Loop a national trail?
Yes. The record marks it as a National Recreation Trail.
Source: Forest Service trail layer
Who manages the South O'Brien Loop?
Lolo National Forest, Forest Service unit 0116. The trail is in Montana.
Is there a fire near the South O'Brien Loop?
4 active incidents within 50 miles of the trail midpoint as of 2026-09-17, the nearest Bison Range Br2F Rx at 35 miles. Check the forest's closure orders before you go.
Source: Fire nearby
Source
This page is built from 1 segment named SOUTH O'BRIEN LOOP in the Forest Service TrailNFS_Publish layer, administrative unit 0116. Wilderness overlap is tested against the National Wilderness Preservation System layer from Wilderness Connect. Trailheads and Forest Service campgrounds come from the Forest Service Recreation Opportunities layer. Data refreshed September 17, 2026. The methodology page explains how segments become trails.