Area used by male and female Phrynosoma mcallii (Hallowell) was studied in a population locted on the Barry M. Goldwater Aerial Gunnery Range near Yuma, Arizona. Area used by males and females shifted through time and did not fit the definition of home range. Summer male and female area used was not significantly different (F=2.625, df=1, P=0.131), but male areas used were significantly larger for 15-day time periods (F=9.67, P=0.0003). Males overlapped the area they occupied in consecutive 15-day time periods more often than did females. Female area used never overlapped within a 15-day time period. Male area used overlapped those of other males and females within a 15-day time period.