Trophic relationships of rabbits [Sylvilagus spp.] black-tailed jack rabbits [Lepus californicus], pronghorn [Antelocapra americana], sheep [Ovis aires] and cattle [Bos taurus] were examined on the Idaho National Engineering Laboratory Site in southcentral Idaho. Grasses were the most important foods of lagomorphs and livestock. Proghorn depended mostly on basin big sagebrush [Artemisia tridentata], common winterfat [Eurotia lanata] and saltbushes. If jack rabbits increase in the future, severe competition for forage with livestock may result.