USFS National Forest System Trails · Helena-Lewis and Clark National Forest · Montana · Updated June 2026
South Grassy Mt (USFS trail 122) is a 6.3 mi trail in Helena-Lewis and Clark National Forest, Montana. Mountain bikes are designated as allowed year-round, with Class 1 e-bikes also designated.
Can I bike South Grassy Mt?
| Use | Status | Season on record |
|---|---|---|
| Mountain bike | Allowed | year-round |
| Class 1 e-bike (pedal-assist, 20 mph) | Allowed | May–Dec |
| Class 2 e-bike (throttle, 20 mph) | Allowed | May–Dec |
| Class 3 e-bike (pedal-assist, 28 mph) | Allowed | May–Dec |
Zooming out: across Helena-Lewis and Clark National Forest, 91% of rideable trail miles are open to mountain bikes — a Bike Access Grade of A.
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About this trail
South Grassy Mt (USFS trail 122) is a 6.3 mi trail in Helena-Lewis and Clark National Forest, Montana. The figures here are pulled from the official US Forest Service trail data for Helena-Lewis and Clark National Forest, covering the trail's mileage, tread, grade band, and the bike and e-bike uses the agency lists as designated. Underfoot, the trail is recorded as native material. No grade band is recorded, so a steepness-based difficulty isn't available for this trail. Mountain bikes are allowed, open year-round in the data. The record additionally permits Class 1, Class 2, Class 3 e-bike use, May–Dec; 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 1 on the agency's 1-to-5 development scale, where 1 is the most primitive, minimally maintained tread and 5 is the most developed. For day-of certainty on closures or seasonal orders, check directly with the ranger district, since this reflects the USFS data as of the latest refresh.
Frequently asked questions
- Can you mountain bike on South Grassy Mt?
- Yes. Mountain bikes are designated as allowed on South Grassy Mt in Helena-Lewis and Clark National Forest, year-round, per USFS data.
- Are e-bikes allowed on South Grassy Mt?
- Class 1, Class 2, Class 3 e-bikes are designated on South Grassy Mt in the USFS data.
- How long is South Grassy Mt?
- South Grassy Mt measures about 6.3 mi in total, summed across its mapped National Forest System segments.
- What is the surface of South Grassy Mt?
- USFS data records the tread surface of South Grassy Mt as native material.
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 Helena-Lewis and Clark National Forest (USFS trail geometry isn't mapped).
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