We examined temporal breeding patterns of bighorn sheep (Ovis canadensis) in the Peninsular Ranges of California to determine the degree of seasonality and identify potential selection for seasonal breeding in this low-latitude desert environment. During a 4-year period, births occurred during 7 months of the year, but 87% of young were born in February–April and 55% were born in March. Peak months of mating and parturition remained relatively constant across years and among different regions of the Peninsular Ranges, and young born in February through April had greater survival than those born later. Female age influenced lamb survival but not timing of parturition. Successful recruitment of young by an adult female had a weak but significant negative effect on the survival of that female's offspring the following year. Previous reproductive history of a female did not influence offspring production or timing of parturition. Months of peak parturition followed annual winter rains and, therefore, were likely to coincide with periods of high plant productivity. Furthermore, most young were born before the hot, arid summer months. We concluded that bighorn sheep in the Peninsular Ranges are seasonal breeders and that climate patterns likely act as ultimate factors in shaping the breeding season.