Thinhorns graze on broad-leaved plants in spring and summer and grasses in the winter. They also eat tender twig tips in winter as they are both grazers and browsers. Thinhorns are usually found in bands of six or more. In the fall, the sexes band together and rams compete by head-butting for dominance and the right to breed with the females. In early summer, after lambing, rams head for higher elevations, often singly or in small groups.

Horns: Both sexes have horns; however, the rams have longer, heavier horns that spiral widely. The horns of a ram can reach 44 in. (111 cm) from base to tip but the bases are smaller than in bighorns, reaching 14 in. (35 cm) in diameter. The ewes' horns are generally only 10 in. (25 cm) long and are similar to the bighorn ewe. The annuli can be used to age a ram. As with bighorn ewes, the annuli on thinhorn ewe horns do not reliably reflect the animal's age.

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