South Fork Plunge

Documentation record: South Fork Plunge has no documented pool or public soak today. This page records what the official geothermal registries and the 1970s agency record say about the spring, and nothing beyond it.

South Fork Plunge appears in the federal thermal springs list at 129 °F (54 °C), on the South Fork Salmon River below Warm Lake in Valley County, and the U.S. Geological Survey’s GEOTHERM file carries the same spring at the same temperature in T15N R6E Sec 14. Most names in those registries are only names. This one was a place: the University of Idaho’s 1972 geothermal inventory lists it in its table of Idaho geothermal developments, and a plunge in that table means a developed swimming and soaking pool, not a wild vent.

The Forest Service record from the same years agrees. The agency’s South Fork Salmon River fishery study (Platts, Progress Report II, 1972) photographs a “Road to South Fork Plunge” in 1967 and again in 1972, and runs a study station “Below South Fork Plunge Bridge.” A road and a named bridge served the site by the late 1960s. What no source documents is anything after that era: no pool, no visit, and no public soak appears in any modern record, and the current agency project for the site proposes removing the bridge and the road. Read this page as a documentation record for a real spring with a real, briefly documented history, not as a destination guide.

Soak Stats

Place Information

Location and Access

The spring sits on the South Fork Salmon River in the Warm Lake country of Valley County, in T15N R6E Sec 14, one section of river corridor the federal inventory found crowded with hot water: GEOTHERM carries four thermal records there, including this spring, a second unnamed vent named for the Plunge (55 °C), and the separate Molly’s springs to the north. It is National Forest country with private summer-home inholdings along the river, working watershed rather than a developed recreation corridor.

Beyond that, this listing deliberately does not go. No published route to the spring exists, no agency presents it as a place to visit, and the status of the old access is itself in question: the Boise National Forest’s South Fork Plunge Watershed project (Cascade Ranger District) would decommission NFSR 490 and remove the old bridge, its abutments, and road fill from the river’s floodplain. The project was listed On Hold in the forest’s 2025 schedule of proposed actions, and whether any part has been carried out is not verified. The coordinates are public record in the registries linked above, but a set of coordinates is not an invitation. Anyone with a genuine reason to visit should establish the current status of the road and the land first, through the Cascade Ranger District.

Is There a Soak Here?

Today, no source describes one. No soaking guide, Forest Service recreation page, or visit account covers a pool at South Fork Plunge in any source consulted, and the documented facts run the other way: a developed plunge existed by 1972, and the agency project for the site now removes its crossing infrastructure. What the plunge consisted of in its working years, who operated it, and when it stopped is a genuinely open question. At 129 °F the source water is properly hot, hotter than an unmixed soak, which fits a developed plunge that once managed it. If a credible field report or a Forest Service update on the watershed project ever surfaces, this page will be updated.

History

The spring’s written record is concentrated in a few years around 1972, and it is a good record. The University of Idaho’s NSF geothermal research completion report (December 1972) lists South Fork Plunge, Valley County, in Table 2, “Location and Name of Geothermal Developments,” alongside Easley Store and Plunge, Silver Springs Plunge, the Cascade City Pool, and Riggins Hot Springs: the developed soaking places of the survey era. The Forest Service’s own fishery study from November 1972 photographed the road to the plunge twice, in 1967 and 1972, and set a study station below South Fork Plunge Bridge, so the crossing and the road were established features of the corridor by the late 1960s.

The registries then carry the spring forward on paper. GEOTHERM holds it as record 0081289 at 54 °C, matching the federal list’s 129 °F exactly, and holds a second, unnamed vent in the same section under the Plunge’s name. In the modern agency record the place name survives mainly as a project title: the watershed restoration that proposes to take the old bridge out of the floodplain. Nothing consulted records when the plunge closed, what became of its pool, or whether any structure survives. That silence is part of the record, and this listing leaves it standing rather than filling it in.

Nearby Hot Springs

The same section of the South Fork holds Molly’s Hot Springs, a separate and hotter inventoried spring about three quarters of a mile north, with its own listings on this site (Molly’s Hot Springs, Molly’s Tubs, Molly’s Toe, and By Golly Molly). The two names share a township section and nothing else; none of the Molly’s pools, tubs, or access belongs to this record. Vulcan and Trail Creek, in the same Warm Lake cluster, are separate springs with their own pages. More West-Central Idaho hot springs →