We used microhistological analysis of fecal pellets to identify plant species in diets of desert mule deer (Odocoileus hemionus eremicus) in southeastern California and to investigate seasonal changes in use of forage classes. We identified 34 taxa of plants, 7 of which have not been reported previously in the diets of desert mule deer. Browse species were abundant in diets during all seasons, but were lowest in spring, when forb species were most commonly observed. Use of succulents generally was low, with highest use occurring in autumn (3 to 24%). Grasses composed ≤1% of the diet in all seasons. Our findings emphasize the diversity of plant species used by desert mule deer and, consequently, the importance of conserving habitats that provide for that diversity.