Mammoth Hot Springs
The terraces and dripstone structures built over the years at Mammoth Hot Springs present an impressive sight. Mammoth is underlain by limestone rather than volcanic rock. So unlike many other springs in Yellowstone, the waters here are rich in carbonate and sulfate, poor in silica. These terraces are built of calcium carbonate (travertine) instead of the siliceous sinter commonly found elsewhere. The white of the travertine contrasts with the oranges, pinks, yellows, and browns created by the algae, bacteria, and some mineral deposits. The geometry of the terraces is constantly changing as a result of the balance between deposition, as the activity in a spring varies, and erosion from the slightly acidic rainwater. Canary Spring, on the upper terrace, is growing and engulfing trees once living only adjacent to, not in, the spring.
No geysers exist at Mammoth because the limestone is too soft to allow the build-up of pressure that a geyser requires, and adequately superheated water is absent.