Isotopic data (δ 13C and δ 18O) for 25 enamel samples from Mammuthus columbi for 13 Mexican localities are provided. On average, the samples provide evidence of a mixed C 3/C 4 diet. The population consists of six individuals with an exclusive C 4 plant diet, and 19 with some consumption of C 3 plants. Latitude, longitude, and elevation do not have an affect on the average diet. Comparisons of data from the Mexican specimens with those values in the literature for samples from California, Arizona, Florida, Nevada, New Mexico, and Texas (USA) show that food habits in North America were similar. Comparisons of δ 13C and δ 18O values with those of javelinas, mastodonts, tapirs, and white-tailed deer from the Floridan Late Pleistocene confirm that mammoths primarily were inhabitants of open areas, indicating a probable case of biomic specialization.