In winter these massive ranges form a barrier against the storms that sweep in from the northwest. More important—these great storehouses of our natural resources that in early days meant only gold and furs, and perhaps sudden death to the pioneers, have now been unlocked by their descendants. The glitter of gold and the glamour of furs pales when contrasted with the untold values that have since been taken out in the baser metals and lumber. This phase too is now coming to an end. It is becoming evident that in the face of our ever increasing population these natural playgrounds are destined to become a buffer against the tensions that we, as one of the most highly civilized peoples of the world, undergo in our daily life. Within another century they will represent one of the few remaining opportunities for many millions of Americans to get close to nature. As such the proper development and preservation of mountainous areas and their values is of vital importance to our Nation.
Mountains of the Southwestern States have been formed by three major agencies. These are, in order of importance, shrinkage of the earth’s interior to form wrinkles on the surface; faulting, with subsequent erosion of exposed surfaces; and volcanic action. The first method is responsible for most of the large ranges, such as the coastal mountains of California and the Rocky Mountains. Faulting is responsible for many of the high plateau areas where one side may be a high rim or cliff and the other a gently sloping incline. The Mogollon Rim, extending across a part of Arizona and into New Mexico, is a classic example in this category. Volcanic action may result in great masses of igneous rock being extruded through cracks in the earth’s surface or it may take the form of violent outbursts in one comparatively small area. Several mountain regions in Arizona and New Mexico are covered with huge fields of extruded lava. Capulin Mountain in New Mexico is an example of a recent volcano which built up an almost perfect cone of cinders and lava. Less noticeable than the mountains, but important nevertheless, are the tablelands of the Southwest. These mesas, too high to be typical of the desert, and in most cases too low to be considered as mountains, partake of the characteristics of both.
Desert “Islands”
The mountains of the Southwest have been compared to islands rising above the surface of a sea of desert. This is an apt comparison for not only do they differ materially from the hot, low desert in climate, but also in flora and fauna. Few species of either plants or animals living at these higher altitudes could survive conditions on the desert floor with any more success than land animals could take to the open sea. Their death from heat and aridity would only be more prolonged than that by drowning. Thus certain species isolated on mountain peaks are often as restricted in range as though they actually were surrounded by water. At times this results in such striking adaptation to local conditions that some common species become hardly recognizable. This is the exception to the rule however; most of the animals in this book are either of the same species as those in the Northern States or so closely allied that to the casual observer they will seem the same. Conditions that enable these species ordinarily associated with the snowy plains of the Midwest and the conifer forests of the North to live in the hot Southwest are brought about either directly or indirectly by altitude.
Life Zones
There are in this nucleus of four States a total of six life zones, (See map on [page x].) The two lowest, the Lower and Upper Sonoran Life Zones, range from sea level to a maximum elevation of about 7000 feet. These two have been covered in the book “Mammals of the Southwest Deserts.” The remaining four—Transition, Canadian, Hudsonian, and Alpine Life Zones—will furnish the material for this book. The names of these zones are self explanatory, because they are descriptive of those regions whose climates they approximate. Unlike the two life zones of the desert, which merge almost imperceptibly together, these upper zones are more sharply defined. They may often be identified at a great distance by their distinctive plant growth. It should be noted that plant species are even more susceptible to environmental factors than animals and are restricted to well defined areas within the extremes of temperature and moisture best suited to their individual needs. Thus each life zone has its typical plant species, and since animals in turn are dependent on certain plants for food or cover, one can often predict many of the species to be found in an individual area.
The Transition Life Zone in the Southwest usually lies at an altitude of between 7000 and 8000 feet. It encompasses the change from low trees and shrubs of the open desert to dense forest of the higher elevations. It is characterized by open forests of ponderosa pine usually intermingled with scattered thickets of Gambel oak. These trees are of a brighter green than the desert growth but do not compare with the deeper color of the firs that grow at a higher elevation.
The Canadian Life Zone begins at an altitude of about 8000 feet and extends to approximately 9500 feet. The Douglas-fir must be considered the outstanding species in this zone although the brilliant autumn color of quaking aspens provides more spectacular identification of this area during the fall. Through the winter months when this tree has shed its leaves, the groves show up as gray patches among the dark green firs. At this elevation there is considerable snow during winter and correspondingly heavy rainfall in summer months. Under these favorable conditions there is usually a colorful display of wildflowers late in the spring.
The Hudsonian Life Zone is marked by a noticeable decrease in numbers of plant species. At this altitude, (9500 to 11,500 feet), the winters are severe and summers of short duration. This is the zone of white fir which grows tall and slim so to better shed its seasonal burden of snow and sleet. In the more sheltered places spruce finds a habitat suited to its needs. Near the upper edge of the Hudsonian Life Zone the trees become stunted and misshapen and finally disappear entirely. This is timberline; the beginning of the Alpine Life Zone, or as it often called, the Arctic-Alpine Life Zone.
Here is a world of barren rock and biting cold. At 12,000 feet and above the eternal snows lie deep on the peaks. Yet, even though at first glance there seems to be little evidence of life of any kind, a close scrutiny will reveal low mat-like plants growing among the exposed rocks and tiny paths leading to burrows in the rock slides. Among the larger mammals there are few other than the mountain sheep that can endure the rigors of this inhospitable region.