The surface expression of the geothermal system consists of a ", opaline sinter terrace produced by hot spring and natural geyser (sic fumarole) activity along the base of the Malpais Rim. Since 1959, several companies have tested the potential of the area as a source of steam for electrical power generation. The spectacular hot water and steam plume that are present at(1985/1986) vents continuously along the top of the sinter terrace is not a natural geyser, but is a free-flowing, uncapped geothermal well." (Struhsacker, 1986, p. 111).