The summit life zone in the Rocky Mountains not only sweeps up to exceptionally high altitudes, but it embraces vast territory. In Colorado alone the Arctic-Alpine territory above the tree-line probably extends over five million or more acres. Thrust high in this summit area are the tops of more than three hundred peaks. Many of these tower three thousand feet above the timber-line. Much of this region is made up of steep slopes, shattered summits, and precipitous walls, many of which bound cañons. There is a scattering of lakes, gentle slopes, stretches of rolling moorlands, and bits of wet meadow or arctic tundra. In this high and far-extending mountain land one may travel day after day always above the uppermost reaches of the forest. In this strange treeless realm there is a largeness of view. Up close to the clouds and the sky, the big world far below, the scene stretches away in boundless, magnificent distances. The snow-fall of this region varies with locality, and ranges from a few feet up to fifty feet annually. In most localities this snow is rapidly evaporated by the exceedingly dry air of the heights. The remnants of each year's fall commonly rest upon the accumulations of preceding years, but during midsummer not one tenth of the heights is snow-covered. Vast areas are occupied by craggy peaks and barren rock-fields. The barrenness is due almost entirely to a lack of soil, not to altitude nor to the rigors of the climate. The climate is in many respects similar to that which wraps the Arctic Circle near sea-level, and it allows many forms of vigorous life. Numerous moraines, terraces, steppes, and moorlands--the wide sky plains--have their soil, and this in the warmth of summer generously produces green grass and brilliant flowers. These, together with big game, birds, and circling butterflies, people this zone with life and turn the towering and terraced heights into the rarest of hanging wild gardens. In favored places for a mile or so above timber-line are scattered acres of heathy growths. Stunted by cold, clipped off by the wind, and heavily pressed by the snow, these growths are thickly tangled, bristly, and rarely more than a few inches in height. Among these are wintergreen, bunchberry, huckleberry, kalmia, currant, black birch, and arctic willow. There are miles of moorlands covered with short, thin grasses, while deeply soil-covered terraces, cozy slopes, and wet meadows have plushy grass carpets several inches thick. These growths form the basic food-supply of both the insects and the warm-blooded life of the heights. [Illustration: ALPINE PASTURES ABOVE TIMBER-LINE Near Specimen Mountain in the Rocky Mountain National Park]