Field-based geologic mapping has identified one large central volcano and 84 small volcanoes and intrusions in an area of 180 mi2 (470 km2) on and near the Mogollon Rim in the north part of Verde Valley, Arizona. Geographic coherency of the volcanic structures and alkaline lava compositions that are markedly undersaturated in silica characterize this volcanic terrane, which, informally, is named the north Verde volcanic field. The volcanic field projects into the Arizona Transition Zone from the southern Colorado Plateau as an alkaline appendage of the basaltic Mormon volcanic field. Transitional and subalkaline igneous-rock series are also represented. Ages of the volcanic rocks are Middle to Late Miocene.