Strictly speaking, all hydothermal features in Yellowstone are hot springs. However, the term is used commonly to denote two specific types of hot springs in the park. The springs that flow and form terraces, such as those at Mammoth, and the springs that appear as pool of hot water in many geyser basins.

At Mammoth, the underground plumbing system of the hot springs runs through relatively soft limestone (calcium carbonate). The soft rock and the numerous openings to the surface do not allow great pressure to build up as they do in geysers. Instead, carbon dioxide gas (CO2) issuing from hot volcanic rocks below the surface bubbles up through sub-terranean ground water forming carbonic acid. This hot acid then rapidly dissolves large quantities of limestone. The Mammoth Hot Springs are formed where this lime-saturated water has seeped down slopes and out upon the surface. Once on the surface the acid cools giving off carbon dioxide gas thus diminishing its power to keep limestone in solution. The limestone is precipitated, building the beautiful travertine terraces.

The hot springs, in the form of pools, found in geyser basins are similar to geysers except that they do not erupt. Their plumbing system is lined with hard geyserite deposits and their cones and basins are formed of the same material. However, these hot springs dissipate sufficient heat by boiling and by surface evaporation that they avoid the tremendous steam explosions that cause geysers to erupt. Also water cooled on the larger surface of the pool settles back down into the plumbing system and helps maintain equilibrium. Slight changes in the plumbing system or in the heat source can cause any of these hot pools to become a geyser, or vice versa.