Hay stored for prolonged periods of time decreases in value for feeding livestock. The irrigated Sonoran Desert of southeastern California and western Arizona is the hottest inhabited part of the United States, with summer temperatures routinely exceeding 100°F from May through October. We evaluated the effects of three methods of hay storage there during the summer: uncovered, under a roof and under a tarp. After 21 weeks, hay that was protected from summer solar radiation, either by the use of barn storage or plastic tarps, had more digestible content.