USFS National Forest System Trails · Flathead National Forest · Montana · Updated June 2026
Lower South Fork (USFS trail 1155) is a 2.7 mi trail in Flathead National Forest, Montana. Mountain-bike use here is accepted but discouraged in USFS data, with Class 1 e-bikes also designated.
Can I bike Lower South Fork?
| Use | Status | Season on record |
|---|---|---|
| Mountain bike | Accepted but discouraged | — |
| Class 1 e-bike (pedal-assist, 20 mph) | Allowed | year-round |
| Class 2 e-bike (throttle, 20 mph) | Allowed | year-round |
| Class 3 e-bike (pedal-assist, 28 mph) | Allowed | year-round |
Zooming out: across Flathead National Forest, 27% of rideable trail miles are open to mountain bikes — a Bike Access Grade of C.
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About this trail
Lower South Fork (USFS trail 1155) runs 2.7 mi through Flathead National Forest in Montana. The figures here are pulled from the official US Forest Service trail data for Flathead National Forest, covering the trail's mileage, tread, grade band, and the bike and e-bike uses the agency lists as designated. The tread is mapped as native material. Based on slope, this is a Intermediate trail (grade band 10-12%); that reflects moderate gradient and is not the same as a technical MTB difficulty rating. For traditional mountain bikes, use is discouraged according to USFS data. The record additionally permits Class 1, Class 2, Class 3 e-bike use; recall that Class 1 is pedal-assist, while Class 2 adds a throttle and Class 3 a higher cutoff speed. The route is mapped as USFS Trail Class 3 on the agency's 1-to-5 development scale, where 1 is the most primitive, minimally maintained tread and 5 is the most developed. Treat this as a planning reference rather than a live conditions report, and verify any time-sensitive closure or order with the ranger district that manages Flathead National Forest.
Frequently asked questions
- Can you mountain bike on Lower South Fork?
- Mountain-bike use on Lower South Fork is discouraged in USFS records, though Class 1 e-bike use is designated. Confirm current rules with the managing ranger district.
- Are e-bikes allowed on Lower South Fork?
- Class 1, Class 2, Class 3 e-bikes are designated on Lower South Fork in the USFS data.
- How long is Lower South Fork?
- Lower South Fork measures about 2.7 mi in total, summed across its mapped National Forest System segments.
- What is the surface of Lower South Fork?
- USFS data records the tread surface of Lower South Fork as native material.
- How difficult is Lower South Fork?
- Its grade-based difficulty is Intermediate (grade band 10-12%), derived from USFS slope data. This reflects steepness, not technical mountain-bike difficulty.
How we read this data
Grade-based difficulty above is the USFS grade (route steepness), not a technical mountain-bike rating — a gentle-grade trail can still be rocky or technical, and vice versa. Bike and e-bike status come verbatim from the USFS managed-use fields for this trail; we never infer access we can't cite. See our methodology for how the dataset is built and what each field means.
Where it is
Approximate location of Flathead National Forest (USFS trail geometry isn't mapped).
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