The Arlington and Gillespie volcanoes west of Buckeye in western Maricopa County, Arizona, form the northeastern part of a string of basaltic volcanoes that include the extensive Sentinel volcanic field west of Gila Bend (Fig. 1). Potassium-argon geochronologic age determinations indicate that basaltic volcanic activity occurred between about 1 and 4 Ma, with significant variation between different eruptive centers. This review is intended to provide basic information regarding geologically recent volcanic activity near the Palo Verde Nuclear Generating Station, and is intended to contribute to a re-evaluation of geologic hazards in the general area. The Sentinel – Arlington volcanic field The Sentinel – Arlington volcanic field extends over about 80 km from Sentinel volcanic field west of Gila Bend northeastward to Arlington volcano west of Buckeye (Richard et al., 2000; Cave and Greeley, 2004). Volcanic rocks in the field are olivine-clinopyroxene basalts that form low relief lava flows and low shield volcanoes, with little evidence of pyroclastic activity (Lynch, 1989; Nealey and Sheridan, 1989; Cave and Greeley, 2007). SiO2 content is ~45-52% (Leeman, 1970; Cave et al., 2007), and 87Sr/86Sr of one sample is 0.7035 (Leeman, 1970). It does not appear that any intermediate or felsic volcanic rocks were erupted in the field.