Diets of sheep on California annual range in the northern Coast Mountains were evaluated at various seasons and stages of plant growth on grass-woodland and improved grassland grazed yearlong at three grazing intensities. Nutritive content of forage samples collected by esophageal-fistulated ewes, including organic matter digestibility, digestible energy, crude protein, ether extract, fiber constituents and minerals, was compared with nutritive content of herbage from both range (vegetative cover) types and with nutrient requirements of sheep. Diets from grassland improved by seeding to subterranean clover were more digestible and had more crude protein and digestible energy than diets from woodland range. There were differences in contents of various nutrients among seasons and phenological stages (e.g., more protein and energy in fall and winter than in summer) but not among grazing intensities. Based on nutrient concentrations, diets were generally adequate for brood ewes except at plant maturity on woodland range when protein and energy could be deficient. Grazing selectivity occurred for some nutrients but not consistently. Associations among nutritional variables suggested that acid detergent fiber was a good indicator of forage nutritional value. Acid detergent lignin and cellulose were the best predictive variables for organic matter digestibility.