USFS National Forest System Trails · Eldorado National Forest · California · Updated June 2026
Thunder Mountain Loop (USFS trail 17E22) is a 8.1 mi trail in Eldorado National Forest, California. Mountain bikes are designated as allowed year-round, with Class 1 e-bikes also designated.
Can I bike Thunder Mountain Loop?
| Use | Status | Season on record |
|---|---|---|
| Mountain bike | Allowed | year-round |
| Class 1 e-bike (pedal-assist, 20 mph) | Allowed | Apr–Dec |
| Class 2 e-bike (throttle, 20 mph) | Allowed | Apr–Dec |
| Class 3 e-bike (pedal-assist, 28 mph) | Allowed | Apr–Dec |
Zooming out: across Eldorado National Forest, 94% of rideable trail miles are open to mountain bikes — a Bike Access Grade of A.
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About this trail
Thunder Mountain Loop (USFS trail 17E22) is a 8.1 mi trail in Eldorado National Forest, California. Everything below comes straight from the US Forest Service National Forest System Trails dataset — length, surface, slope-derived difficulty, and the specific bike and e-bike designations on record — so you can check legality before you load up. The tread is mapped as native material. Its grade-based difficulty is Advanced (grade band 12-20%) — a steep steepness profile derived from USFS slope data, not a technical mountain-bike rating. Bike use is designated as allowed year-round. On the electric side, Class 1, Class 2, Class 3 e-bikes are also designated (Apr–Dec) — Class 1 being pedal-assist only, Classes 2 and 3 adding a throttle and higher assisted 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. 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 Thunder Mountain Loop?
- Yes. Mountain bikes are designated as allowed on Thunder Mountain Loop in Eldorado National Forest, year-round, per USFS data.
- Are e-bikes allowed on Thunder Mountain Loop?
- Class 1, Class 2, Class 3 e-bikes are designated on Thunder Mountain Loop in the USFS data.
- How long is Thunder Mountain Loop?
- Thunder Mountain Loop measures about 8.1 mi in total, summed across its mapped National Forest System segments.
- What is the surface of Thunder Mountain Loop?
- USFS data records the tread surface of Thunder Mountain Loop as native material.
- How difficult is Thunder Mountain Loop?
- Its grade-based difficulty is Advanced (grade band 12-20%), 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 Eldorado National Forest (USFS trail geometry isn't mapped).
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