[en] An aerial survey of terrestrial gamma radiation was performed during the period 4 November through 15 November 1982 over a 16-kilometer by 16-kilometer (10-mile by 10-mile) area approximately centered on the Palo Verde Nuclear Generating Station near Wintersburg, Arizona. Gamma radiation spectral data were collected while flying a helicopter over a regular pattern of parallel lines spaced 150 meters (500 feet) apart at an altitude of 90 meters (300 feet). All radiation measurements taken at the nominal flight altitude were corrected for altitude variations, cosmic radiation, and helicopter background to generate exposure rates from terrestrial sources extrapolated to 1 meter above ground level. The data are presented as isoradiation contour maps. The average terrestrial radiation levels fall between 8 and 14 microrentgens per hour (μR/h). All gamma radiation detected within the survey area was associated with naturally occurring radionuclides. Direct ground-based measurements at 1 meter height were also taken at four scattered sites within the survey area. These values agree with the contour intervals determined from the aerial measurements and differ from the mean value of adjacent contours by no more than 10%. 6 references, 5 figures, 2 tables