These vegetation zones should not be visualized as nice neat bands on the mountainsides, however, for roughness of topography and differing tolerances of plant species usually lead to gradual changes from one zone to the next. Because of the greater exposure to drying heat and sunlight, each belt occupies a higher range of elevation on south-facing slopes than on north-facing ones. And along draws, where conditions are wetter and cooler than on ridges at the same elevations, the vegetation zones finger down to lower elevations; on ridges the opposite is true. Animals are less restricted than plants to particular vegetation belts, but they, too, show a zonation with altitude. You must look, for instance, in the paloverde-saguaro community (part of the desert scrub type) for kangaroo rats and cactus wrens; in the oak-pine woodland for Mexican jays; and in the ponderosa pine forest for whitetail deer and tassel-eared squirrels. In the Tucson Mountains, only the desert scrub type is well represented, although the highest ridges support a suggestion of desert grassland. A small patch of shrub live oaks, relicts of a wetter period, huddles on the north side of Wasson Peak. Zonation is poorly developed here because the mountains are low and small in mass. (Studies have shown that mountains of smaller mass tend to have warmer and drier climates than bulkier mountains of the same height.) Major Vegetation Types in Saguaro National Monument Vegetation type Average Elevations Annual Life zone July (feet) rainfall temp. (inches) Prominent species Southwestern Desert 94 2,200 to 4,000 7 to 13 Lower Sonoran Scrub Paloverde Saguaro Pricklypear Cholla Catclaw Ocotillo Creosotebush Mesquite Ironwood[1] Grassland Transition 85 3,500 to 4,500 10 to 15 Upper Sonoran Mesquite Beargrass Gramagrasses Amole Sotol Oak-pine-juniper 74 4,500 to 7,000 12 to 22 Upper Sonoran Woodland and Chaparral Emory Oak