The presence of the limestones and sandstones indicates that that area was submerged below the water of ancient seas one or more times in the geologic past. The gneiss, schist, and granite bespeak deep-seated metamorphism and magmatic intrusion, which gave these rocks the form, composition, and texture they possess today. The lava flows are indicative of volcanic activity that was a part of the extensive volcanism that occurred in this part of southern Arizona. And, finally, the great alluvial fans and bajadas suggest that these mountain ranges could bury themselves in their own products of erosion unless the mountain-building processes in future eons continue at a faster pace than the wearing-down processes. This evidence enables us to perceive today’s landscape as but a transitional phase in the drama of change that will continue for milleniums. [Illustration: Chiminea Creek, originating in the higher elevations of the Rincon Mountains, forms a ribbonlike oasis of hydrophytic plants, including large trees such as sycamore, walnut, and cottonwood.] plant and animal zones Mountains are biologically exciting because their elevation produces, in a short vertical distance, the same climatic changes that occur over long latitudinal distances. In Arizona, average temperatures drop about 4° with each 1,000-foot rise in elevation, and precipitation increases about 4 to 5 inches. At sea level, you would have to travel about 900 miles north to experience the climatic change found in going from the lowest part of the monument (2,200 feet) to the top of Mica Mountain (8,600 feet). Plant-and-animal communities change along these climatic gradients. In southern Arizona, the sequence of vegetation types begins with desert scrub at the lowest elevations, and ranges through desert grassland, oak woodland and chaparral, oak-pine woodland, ponderosa pine forest, and Douglas-fir forest, to Engelmann spruce forest on top of the highest mountains. In the national monument, we have all these types except the last—although desert grassland is poorly represented here because the steep slopes squeeze it into a narrow altitudinal band; and Douglas-fir forest is restricted to small areas in canyons and on north-facing slopes at high elevations. A few drainageways (notably Chiminea Canyon, on the south side of the monument) support patches of deciduous trees classified as riparian woodland.