The Hopi Buttes dominate the landscape north of Holbrook, Arizona, commonly rising to heights of 180 m above the surrounding countryside. The buttes are underlain by individual diatremes, or in some cases by a complex of diatremes. Some sediment-filled diatremes also crop out as inconspicuous low hills (some may also be buried beneath the alluvium). The diatremes erupted into the late Miocene-early Pliocene Hopi Lake. No region in the world is known to contain a greater density of diatremes than the Hopi Buttes, where more than 300 diatremes occur within about 2500 km2. The diatremes of the Hopi Buttes are somewhat unique; they, along with few others, most notably the Miocene diatremes of the Schwabian Alb, formed maars in which lacustrine sediments accumulated. These lacustrine sediments were the hosts for syngenetic uranium mineralization. The funnel-shaped vents are filled with limburgite tuff and tuff breccia, agglomerate, monchiquite dikes, necks, and flows, fine-grained clastic and carbonate rocks, and blocks of sedimentary rocks, especially the Wingate Sanstone, derived from the vent walls.
