Angel Terrace is located within the upper (southern) part of the greater Mammoth Hot Springs thermal basin. These travertine terrace deposits form where hot water saturated with dissolved calcium and bicarbonate migrates to the surface. As spring water spills over the lip of the pools, carbon dioxide escapes as gas, and calcium carbonate is precipitated (forming travertine). Active terraces are rapidly changing. Note the dead trees in the background (they were killed by the surrounding buildup of mineral deposits). The buildup of travertine has been measured in as much as eight inches-per-year.