Anthophorids are a species-rich and widely distributed group of solitary bees.   They typically are moderately large, with considerable 'hair' and 'fuzz' on the body.   I don't know which one this is, but it may be one of the many species of Diadasia.   These were resting or sunning on various flowers, including cactus blossoms, in the UC Riverside Botanic Gardens.