H is for hot springs

In the Idaho-based world of New Grass Growing (and River and Ranch) there are hot springs. They exist in the real Idaho as well. One of the pleasant outcomes of living in a geologically active setting is hot water. Generally this is because geologic activity tends to generate heat. Plate subduction, terrane accretion, plate moving over hot spot, granitic pluton cooling, you know, all the usual suspects.

Water, usually in the form of melted snow, works its way downward through mostly local fractures in overlying material. Heat increases with depth, so the deeper the water goes in proximity to the heat source (e.g. a granitic intrusion like the Idaho batholith) the hotter it gets. Literature fails to provide a consistent explanation for the introduction of water to the system for heating and then a separate exit of the now hot water from the system. Happily for whatever reasons of nature's plumbing, hot springs work.

In the world of River and Ranch and New Grass Growing, you'll find Lolo Hot Springs (most developed), Jerry Johnson's (on the far side of the Lochsa may now have a locked gate), Weir Creek (hardest to get to), Sharkey Hot Springs (out near Cayuse Creek), and the hot springs at the base of Lost Trail Pass. Down the river(s) you encounter Barth, Sheepeater, Sunflower, Hospital Bar and others that at the moment I am forgetting.

They are natural, others don't always leave them clean, and they may have naturally occurring sulphur-centric microbes giving them a distinct odor. So, use at your own risk and please leave them cleaner than you found them. They are really neat places.