There are four major types of basalt and basaltic andesite in the central Cascades: early high-alumina olivine tholeiitic (HAOT) basalt, normal High Cascade HAOT basalt, North Sister basaltic andesites, and Mount Washington type basaltic andesites. Hughes (1990) argues that their differences could be the result of different magma sources or magma evolution in open systems. Mount Washington basaltic andesites are also considered one of the three distinct mafic rock types in the High Cascade platform, with North Sister basaltic andesites and normal basalts. The three groups all exhibit different major and trace element abundances. Mount Washington basaltic andesite is more common than North Sister basaltic andesite, with higher levels of incompatible elements and rare-earth elements. It also extends to the east and west of the major Cascade arc. Otherwise, the Mount Washington and North Sister basaltic andesites display lithologic similarities including a dearth of pyroxene phenocrysts and augite microphenocrysts, and both groups were probably near-primary melts. According to Hughes (1982), examples of Mount Washington basaltic andesites occur at Holocene deposits from Nash Crater, Four-in-One Cone, and Little Belknap Cone, as well as undated deposits at Todd Lake Volcano, Falls Creek, Broken Top, and the abutment of Tumalo Dam.