Regionalism: A Traditional Academic Subject

The first major step toward a geographical regional concept appeared in the works of the German geographers Karl Ritter, in the 1850s, and Friedrich Ratzel, in the 1880s. Further interest in regionalism was revitalized around the turn of the century, again among the Germans. American historian Frederick Jackson Turner, who espoused the "frontier thesis," in 1920 said that as the frontier disappears and "the nation settles down to the conditions of an occupied land, there will be emphasized the sectional differences arising from unlike geographic regions." A now-classic book, American Regionalism, published in 1938 by Howard Odum and Harry Estill Moore, tried to show that regionalism "may be the key to a better understanding of the past and the richer development of the future theoretical study of our society, and to the practical planning of its new frontiers." In 1939, Richard Hartshorne carefully advocated the identification of "regions" so that "we can... seek the most intelligent basis or bases" for dividing the world into manageable areas of study.
Historian Merrill Jensen, who in 1951 edited Regionalism in America, admitted that "the region is a concept that cannot be reduced to simple formulas" and that it "was plain that the concept of 'region' meant different things to different academic disciplines, to administrators of state and federal governments and to executives of great industrial organizations. In other words," Jensen stated, "the nature of a 'region' varies with the needs, purposes, and standards of those using the concept." Nonetheless, Jensen reminded the reader, the very complexity of a regional approach had a "utility both as a tool for research and as an approach to [the day-to-day] problems of public administration."
By 1975, sociologist Nathan Frazer, writing the foreword for Raymond Gastil's Cultural Regions of the United States and contrasting the times with the 1930s, lamented: "American regionalism, it seems, is not much studied these days or if studied is not much in the public eye or the consciousness of opinion-makers." In the same book, Gastil, himself, argued that seeing our society from a regional point of view "may generate new approaches that will lead to [an] improved understanding of ourselves, and in some areas to new social and economic policies."
In 1972, esteemed geographer John Fraser Hart wrote:

Regional geography, the skillful description of areas and places, is the highest form of the geographer's art. A good regional geography can bring an area to life and help us understand and appreciate what it is like, as well as how it came to be. Each region is distinctive and must be understood in its own terms, rather than according to some preconceived checklist. The regional geographer must know the land in all its moods and seasons and be sensitive to the values, aspirations, and talents of the people who live in it.

However, good regional geography, Robert P. Larkin and Gary L. Peters more recently have pointed out, "is also a scarce commodity. All too often," they say, "regional geography amounts to little more than a windy exposition that catalogs everything that exists in a particular place. Thus, the importance of regional research in recent decades has waned, and systematic studies have tended to dominate" the scholarly geographic scene. "Despite changing attitudes and approaches to geographic inquiry," they conclude, "the regional concept remains an important one."


In the past fifteen years an innovative, interdisciplinary, and "holistic" approach to regional studies has attracted a number of devotees. Known as "bioregionalism," this concept identifies geographical regions as areas whose cohesiveness is determined by shared and interrelated physical and cultural traits, as opposed to the traditional and arbitrary definitions established by political boundaries and "popular culture" identities, such as those pop-culture regions identified by Joel Garreau.
The bioregionalists believe that "bioregionalism calls for human society to be more closely related to nature, and to be more conscious of its locale, or region, or life-place.... It is a proposal to ground human cultures within natural systems, to get to know one's place intimately in order to fit human communities to the Earth, not distort the Earth to our demands." These new geographers find bioregional distinctions to be based on climate, biotic patterns and similarities, watersheds, landforms, elevation and physiography, historical and prehistorical activities, shared spiritual presence, and "functional" demographic patterns. In this pursuit, bioregionalists develop analyses of developmental patterns of demographics, human ecology, economics, and politics as they are related to a bioregion's history of natural resource use. In particular, they try to focus on a region's "carrying capacity," "cross-cultural conflicts," and "quality of life" considerations. Students of bioregionalism examine the significance of such bioregional expressions as "point of critical deterioration" and "point of irrevocable deterioration." They ask that human cultural behavior fit in with nature, and they call for political self-government with such bioregions.
About the need for a bioregional understanding, Kirkpatrick Sale has said:

the crucial and perhaps only all-encompassing task is to understand place, the immediate specific place where we live. The kinds of soils and rocks under our feet; the source of the waters we drink; the meaning of the different kinds of winds; the common insects, birds, mammals, plants, and trees; the particular cycles of the seasons; the times to plant and harvest and forage--these are the things that are necessary to know. The limits of its resources; the carrying capacity of its lands and waters; the places where it must not be stressed; the places where its bounties can best be developed; the treasures it holds and the treasures it withholds--these are the things that must be understood. And the cultures of the people of the populations native to the land and of those who have grown up with it, the human social and economic arrangements shaped by and adapted to the geomorphic ones, in both urban and rural settings--these are the things that must be appreciated.

A bioregion "is governed by nature, not legislature," says Sale. "The first law is that the face of the earth is organized not into artificial states but natural regions, and those regions, while varying greatly in size, are mostly much more limited than those defined by national boundaries."
The bioregionalists attempt to present concerns and identities about a region in a way that respects the deeply felt but usually ignored perspectives of the region's native people. As yet, native Southwesterners have had little to say about the region's character and identity; to date and for the most part, the region's identity has come from only tourists and immigrants.
Kirkpatrick Sale has stated that a bioregion is "a life-territory, a place defined by its life forms, its topography and its biota, rather than by human dictates." He goes on to say that

In maps of physiographic provinces and natural vegetation and soil distribution and forest belts and climatic types and riverine systems and land-use variations and all the other natural features the experts have diligently charted you begin to see something almost (appropriately enough) organic. For it turns out that bioregions are not only of different sizes but often can be seen to be like Chinese boxes, one within another, forming a complex arrangement from the largest to the smallest, depending upon which natural characteristics are dominant.

I intend here, to some observable degree, to honor the sensitivity and the sensibilities of the bioregionalists.

The Geometiic Southwest

If "regional studies" have any justification and validity at all, surely there must be some way to ascertain an identification and a definition of where the region is that we want to study--in this case, the "American Southwest." Where is it? What is it? Should we be talking here only about "the contiguous United States" or even "the United States"? Should we acknowledge "impressions" or be limited to a specific and measurable physical geographic place?
Let's assume that we should care about identifying the Southwest as a region.
On a daytime airline flight from, say, St. Louis to Los Angeles, if you have a seat by the window and are curious enough to look out, you cannot, as you travel through the sky, ignore the flat Great Plains below you. And, eventually, on a clear day--a decreasingly frequent condition--you can perceive ahead toward the west the Rocky Mountains rising up roughly and suddenly from the flat plains. Once you are over Las Vegas, New Mexico, there is no doubt that this rugged region is different. West of the Llano Estacado and the Pecos River tones of browns and grays more than greens and blues dominate the land's surface hues. And from the airplane, you also know that you are over the Southwest when you can see the rivers flowing toward the south or west instead of toward the east, cutting down in serpentine cañons from the Rockies through the Rio Grande Trough; the Central New Mexico and Arizona Highlands; and the Colorado Plateau. Mountains, valleys, deserts, and plateaus--these landforms constitute the Southwest, not plains, littorals, swamps, and tundra. The region is simply and observably there.
While the American Southwest's many definitions have varied widely in criteria, concept, and physical location, there are certain qualities associated with the region--empirical and measurable factors--that would, given the chance, receive a consensual endorsement. For instance, most people would agree that such physiographic features as rugged mountains, rocky canyons, dry gulches, and unusually high elevations are acceptable traits that characterize the Southwest. Arbitrarily recognizing such climatic qualities as clean, cloudless air, extreme aridity, high summer air temperatures, extreme diurnal (twenty-four-hour) temperature ranges, and a much greater amount of insolation (hours of sunshine per year) than the North American average as reasonably valid Southwestern qualities won't draw much dissent, either. Normally measurable census- type features such as ethnicity, language classification, source of livelihood, and other data--factors that distinguish regions as well as neighborhoods--are "objective," too. There are acceptable empirical departure points. However, it is not proposed here to ascertain "the American Southwest" by "objective" methods alone. "Perceptions" and "impressions," most metaphysicians would concede, mean a lot. But let us start out with a mathematical and quantifiable methodology.
If seriously contemplated, the expression "American Southwest" implies certain very specific, observable, measurable, and graphic characteristics, including traits that are geographic, geometric, and directional. As one segment of the four quadrants of the compass, the Southwest has a location that can be determined simply by dividing the contiguous United States into four geometrically determined sections.
Cartographers have identified a spot less than a mile to the northwest of Lebanon, Kansas, as the geographical center of the "conterminous" or "contiguous" forty-eight United States. Lebanon lies at 39° 55' North Latitude (39° 55' N.) and at 98° 32' West Longitude (98° 32' W.). The number of square miles of the area east of the meridian equals that of the area to the west. Likewise, the region north of 39° 55' N. equals in size the area to the south. The intersection of these two lines creates four quadrants. But these four quadrants are by no means the same size. Due to the physiographic configuration of the United States, the northeast quadrant is much smaller in square miles than the southeast quadrant. Accordingly, the northwest quadrant conspicuously exceeds the southwestern quadrant's size.
So, by logical definition here, the Southwest of the United States, purely in the geometric sense, lies south of 39° 55' N. and west of 98° 32' W. For a start, anyway, these lines should serve as practical--and semantic--reference borders for the location of the American Southwest by providing specific and explicit boundaries and orientation rather than by offering an implied and vaguely identified "region" (see map 1). Any greater effort to employ this methodology of regional division quickly becomes futile if not absurd. For example, as map 2 shows, a hexadic division is patently inappropriate, and any further attempt to use inflexible parallels and meridians becomes even more useless.
The farthest extension westward of the United States' Southwestern quadrant reaches approximately the 124th Meridian W. at Cape Mendocino, California, a physiographic protrusion (124° 20'W.), while the region's southernmost point can be found near the extreme southern tip of the state of Texas, a political boundary, at 26° 10' N., a spot on the Rio Grande about halfway between the towns of Rio Grande City and McAllen. These vertical and horizontal boundaries, in turn, determine the quadrant's geometric center to be 111° 15' W. Longitude, 33° 00' N. Latitude, a place just a few miles east of Florence, Arizona. Many people probably would not find this location to be at all unreasonable (see map 3).
However, for most people concerned about this problem, the coordinates ascertained here must be quite a bit less than satisfying. In many ways, all four sides seem too broadly encompassing. Making the 26th Parallel the region's southern boundary would please Charlie DiPeso and Miguel León-Portilla--but very few other people. Protracted westward, this line would enclose most of northern Mexico, thus including almost as much Mexico as United States within the "Southwest," and thereby discrediting the 26th Parallel's usefulness as a southern boundary for something "American," that is, in this sense, "of the United States." And we must admit few people would agree that a great chunk of the Pacific Ocean--no matter how desirable--belongs in the American Southwest. The same could be said of the California Pacific Ocean littoral or of California's Central Valley and the Sierra Nevada. Certainly, too, the argument to include the Great Plains within the Southwest is a weak one, as is the inclusion of Nevada's and Utah's Great Basin.
Everything considered, this geometrically determined Southwest falls far short of being satisfying. As D. W. Meinig has pointed out, there is "nothing significant in longitude and latitude per se for regional definition." Geographically, Meinig has matter-of-factly observed:

The [quadrant] system is an arbitrary reticule fitted on a globe as a practical device to locate points and has no other intrinsic meaning. When used as an ostensibly handy reference for some significant regional feature it is usually misleading. The United States is roughly a rectangle and thus has a 'southwest,' but that is only significant in some more specific context.

For the moment, however, let us proceed with the geometrically determined Southwestern quadrant as only a starting place, a background, a "context," as Meinig puts it, in which to refine the regional definition more precisely.

The Physiographic Southwest

Many of us have never felt any serious uncertainty about the American Southwest's locale. The Southwest has never existed in Mexico south of the Sonoran Desert or in California west of the Mohave Desert. Little "Southwestern" could be found north of the striking erosion features of the southern third of Utah or in Colorado north of the Arkansas River or in New Mexico east of the Pecos River. If we proceed with these confinements--all of which lie within the geometric Southwest--we can have an even more limited (if still quite general and somewhat vague) set of boundaries. More important, perhaps, it has always seemed to me that unique cultural traits exists only in this physiographic domain so circumscribed. Indeed, it also seemed to me that a cause-and-effect relationship, that is to say, some evidence of environmental determinism, might even possibly be at work here.
Which physiographic traits do characterize the "Southwest's" geography? Certainly not estuaries, swamps, tundras, rolling green hills, archipelagos, broad savannas, moors, coastal plains, clusters of natural lakes, prairies, seashores, lowlands, islands, or coral reefs. Although small bits and pieces of some of these features can be found in the Southwest, they make up the meager exceptions that accentuate the rule. Instead, most people would agree, the Southwest's physiography conspicuously includes high plateaus; steep, deep canyons; rugged mountains; deserts; and basin-and-range "transition" features. And little else. Such uncontestable Southwest features as the Grand Canyon, Bryce Canyon, and Zion Canyon, together with other national parks and monuments such as Carlsbad Caverns, Black Canyon of the Gunnison, Arches, Canyonlands, Death Valley, and Capitol Reef also belong, obviously, to the region. Other larger, broader physiographic features fall within the Southwestern quadrant, too: the Southern Rocky Mountains; the Colorado Plateau; the Mohave Desert; the Sonoran Desert; and the Arizona, New Mexico, and Mexican Highlands, as well as parts of northern Mexico's Sierra Madre Occidental and Chihuahuan Desert (see map 4).
The Southern Rocky Mountains, among the most massive in the United States, extend from north-central New Mexico northward into Colorado (35° N to 390 N.). These mountains rise abruptly west of the Great Plains (105° W.) to altitudes greater than fourteen thousand feet. The Continental Divide lies along the summit of the Southern Rockies, and this line is properly called the Great Divide, since it separates the Atlantic and Pacific Ocean watersheds. Great anticlinal arches and intervening basins characterize the geological structures recurring most often in the Southern Rockies. Most of these structures resulted from an orogeny that probably started in early Cretaceous time and reached its peak in early Tertiary time. Erosion has exposed ancient Precambrian crystalline rocks in the central part of the mountains. Between the mountain ranges, Tertiary and Quaternary terrestrial sediments and volcanics have filled the basins.
In addition to providing runoff for the Arkansas River and its feeder system, which eventually empties into the Mississippi River, the Rockies' southeastern slopes, including the Jémez and Sangre de Cristo Mountains, drain into the Rio Grande and into this river's major tributary, the Pecos River. On the range's west side, the Colorado River and its secondary sources provide much of the drainage--and much of the useful water--for the Southwestern quarter of the United States.

The Rio Grande and Colorado River Drainage Systems as the "Southwest"

If we were to consider only the drainage systems for the Rio Grande and the Colorado River, a solid identification of the physical "Southwest" could be based on these geologic and hydrologic watershed patterns alone. Ethnologist Pliny Earle Goddard wrote in 1931, "The region which is called the Southwest... is a natural geographical division lying [mostly] south of the higher and more definite ranges of the Rocky Mountains. It is drained by the upper portion of the Rio Grande River and its tributary, the Pecos, and by the Colorado River and its three main eastern branches, the San Juan, the Little Colorado, and the Gila." As map 5 indicates, the entire Rio Grande drainage system and all but a small, northern part of the Colorado River system lie within the geometric Southwestern quadrant. Eliminating the Green River branch, which mainly ties north of the Southwestern quadrant, would put the remaining Colorado system entirely within the physiographic Southwest.
The Colorado River watershed is much larger and accepts much more precipitation than does the Rio Grande watershed, although it is true that great amounts of water in the Upper Colorado Basin are diverted across the Continental Divide to the Rockies' eastern rain shadow side. For almost a hundred years power politics have made possible this watershed manipulation in an effort to remedy the Denver area's aridity. Starting in 1892 with the Grand Ditch, a number of dams, reservoirs, tunnels, and canals have been built to bring water over the Divide to the less rainy but more populated Rocky Mountain Front Range. Even though the Upper Colorado River Basin ecology has no doubt suffered considerably from this watershed manipulation, the Colorado River's hydrologic bowl remains well defined. Almost all of the Rio Grande drainage system lies within the physiographic Southwest. However, most of eastern New Mexico drains into the Arkansas River system, which belongs to the Great Plains Region, or it drains into closed basins within the Great Plains.
Quite simply, both the Colorado River and Rio Grande watersheds give preciseness to regional identification. Among the bioregionalists the most conspicuous and most often mentioned bioregion is the watershed. Drainage systems, says Peter Berg, "help to define and tie together the life of the bioregion... [and] the network of springs, creeks and rivers flowing together in a specific area exerts a dominant influence on all non-human life there; it is the basic designer of local life." Bioregionalist Judith Plant believes that communities seem "to most fervently gather around watershed protection activities... because water is absolutely fundamental to survival." And, she goes on to say, a watershed is "a great organizing tool, for it begins to define the natural boundaries of place."
To the west of the Southern Rocky Mountains lies the Colorado Plateau, which has an elevation that averages about five thousand feet above sea level, making this region the nation's highest plateau. The Southwest's largest, most conspicuous, and most dramatic physiographic area, the Colorado Plateau (between 34° and 40° 20' N.L.; 106° 30' and 113° 30'W.L.) possesses most of the spectacular canyons and rock formations for which the Southwest is noted. It covers almost half of the state of Utah and more than a third of Arizona, as well as large portions of Colorado and New Mexico. Along its western and southern edges rise mountains and escarpments that cast a rain shadow on the plateau, limiting precipitation in this physiographic region to an average total of less than six inches annually.
Thick sequences of predominantly sedimentary strata, many of them brilliantly colored and sculptured by local erosion into fascinating and beautiful landscape features, underlie the Colorado Plateau. An almost mile-thick section of these beds is exposed in the walls of the Grand Canyon. In addition to the abundant sedimentary rocks within the province, large areas of volcanic materials, principally lava flows, can be found. The Colorado Plateau ranges in elevation from 5,000 feet to 11,000 feet above sea level.
Although the Colorado River and its tributaries flow through much of the Colorado Plateau, the gorges the rivers have cut and through which they flow in most places have left the streams too far below the surrounding level land surface to enable profitable irrigated agriculture. In addition, the plateau's high elevation narrows its annual growing season considerably. Until recently the scenery here was the region's most valuable economic asset. But in the last fifty years electric-generating plants (both hydro and fossil fuel), uranium mines, coal stripmines, oil wells, and natural gas deposits increasingly have brought income, at least temporarily, to the region's people.
Southwest of the Colorado Plateau, in a counterclockwise direction within the general limits of the Southwestern quadrant, lies the region physiographers have termed the Basin and Range Province. However, most people would recognize this area simply as "desert." The Sierra Nevada Range and the Pacific Border Province form the western boundary of the Basin and Range Province and, therefore, form the western border of the physiographic Southwest. Composed of nearly parallel block-faulted mountains and valleys, the Basin and Range Province includes the most extreme desert region of the Southwest--and of North America. The major desert valleys in the Basin and Range Province, which lie between the 109th and 120th Meridians and south of the 39th Parallel, have specific designations: the Mohave Desert (37° N. to 34° N.) and the Sonoran Desert (34° N. to 30° N.).
Wedged between the Sonoran Desert on the west and on the south and the Colorado Plateau on the north is a region geologists and geographers call a "highlands" region. Located north of the 30th Parallel, most of this region is found in central and southeastern Arizona, where it is called the "transition" region, and in western and central New Mexico, where it is mainly covered by the Datil-Mogollon volcanic field. Similar but smaller landforms exist in northeastern Sonora and northwestern Chihuahua. South of the Mexican Highlands rises the extreme north end of the long geologic spine of northern Mexico--the Sierra Madre Occidental. Starting from the north at the 31st Parallel, for almost a thousand miles this range parallels from northwest to southeast the coastline of the Gulf of California and the Pacific Ocean. To the sierra's east, basin-and-range features reappear. This region, known as the Chihuahuan Desert, lies between the 26th and 34th Parallels and west of the 104th Meridian. Fingers of this desert extend north from Mexico into parts of south-central New Mexico--such as the Tularosa Basin and the notorious Jornada del Muerto--as well as into that area of western Texas adjacent to the Rio Grande. Most of the Chihuahuan Desert ties above four thousand feet. New Mexico's interior highlands province, together with several basin-and-range areas, including the Rio Grande Rift Basin, the Sacramento Mountains Section, and the Pecos Valley Section, connect the Chihuahuan Desert with the Southern Rockies.
Contrary to much popular belief, the low desert of the region--which appears in so much stereotypical Southwest landscape imagery--comprises less than 10 percent of the physiographic Southwest. While much of the Sonoran Desert in Arizona ties below 1,000 feet, the rest of the state has an elevation that averages more than 4,000 feet. In New Mexico, except for a few square miles where the Pecos River flows across the states southern border into Texas, the elevation everywhere is above 3,000 feet. More than half of New Mexico is more than a mile above sea level.
Physiographers usually designate that part of New Mexico found to the east of the Pecos River valley as belonging to the Great Plains. The grasslands situated in east-central New Mexico along the Texas border comprise an area called the Llano Estacado, or "Staked Plain." Despite this Spanish name, however, geographers have found that topographically, economically, historically, and demographically the Llano Estacado has very little in common with the other regions of the Southwest discussed in this essay. A proper eastern physiographic boundary for the Southwest would be the Pecos River or, at most, the 104th Meridian.
In brief, then, the predominant characteristics of the physiographic United States--and, in addition, parts of Mexico--are, counterclockwise from the Great Plains, the Southern Rocky Mountains; the Colorado Plateau; the Mohave and Sonoran deserts; the Central Highlands; the northern Sierra Madre Occidental; and the northern Chihuahuan Desert. Rugged mountains and large rocks; sharp, steep canyons; irregular basins and valleys; wide deserts; high plateaus; small but high-elevation meadows and parks; and hydrologic playas dominate the physiographic Southwest. Quite obviously, America's physiographic Southwestern quadrant possesses distinctive and conspicuous landscape traits that give it a definite regional "identity." Except for the extreme northerly part of the Southern Rocky Mountains and the Colorado Plateau, as well as the southern part of the Sierra Madre Occidental, all of the Southwestern landforms combined lie well within the 26° L.-39° L. north-south boundaries of the American southwest quadrant. As map 4 shows, the 29° physiographic Southwest clearly is situated between 104° and 119° West Latitude.

The Geologic and Climatic Southwest

Awe-inspiring physiographic traits clearly stamp the uniqueness of the Southwest. But the region's climate, too, separates it from the rest of North America--or the world, some would say. Such climatic factors as the degree of cleanliness and crispness of the air, air temperature, temperature ranges, aridity, and insolation (hours of sunshine per year) are measurable factors that identify the region. Although Ross Calvin chose to tell us that "sky determines" the Southwest's unique geographic traits, a closer look would have enabled him to see that land is even more basic than sky. Land lured settlers, both prehistoric and since, to soil that was fertile and minerals that were valuable. Land determined the design and materials for housing and fortifications. Land determined travel and trade routes. Land as much as sky determined lifestyles and "carrying capacity." And in many ways, land also determined the climate. But the land was "determined," too.
The prevailing Southwest climatic pattern appears more standardized and, thus, more predictable than the climate of the remaining country. Most of North America, particularly the United States, experiences a general weather system made up of air masses that move from west to east across the continent. For example, most air-mass movement, including the moist air masses that deliver to the Southwest region its limited precipitation, rarely come to the region from the north, the northeast, or the cast. Therefore, the windward and rainy sides of the Southwest's escarpments and mountains are the south and west sides, while land lying to the north, northeast, or east of these more highly elevated landforms experiences-suffers from, may be more accurate-the "rain shadow" effect. (However, much of the runoff in the Pecos River drainage system-the Rio Hondo Basin, for example-does precipitate on the eastern flanks of New Mexico's east-central highlands region.)

The Geology of the Physiographic Southwest

To understand this phenomenon better, we need to examine the geologic forces in the Southwest that appear to have a strong impact on the region's climate and weather. Most geologists who study this region agree that plate tectonics--the shifting of large, relatively thin segments of the earth's crust--have done the most to create the Sierra Madre Occidental, the Rockies, the Colorado Plateau, and the other conspicuous and dramatic landforms of the Southwest. Specifically, the Pacific Plate and the North American Continental Plate have come in conflict and created tectonic forces that have formed mountain ranges and valleys, ridges, and depressions. Probably for more than two hundred million years the Pacific Plate has pushed, or "subducted," eastward and underneath the North American Continental Plate, which has maintained a relatively inert but nonetheless resistant counterforce. In more recent geologic time, "strike-slip" motions have been more significant than subduction in shaping the Southwest's physiography.
The overall effect of this two-plate confrontation of the earth's crust has caused the North American plate to uplift and retreat, and, as it was forced back, to experience geologic "deformation," a process whereby layers of rock compress, rise, fold, fall and, in some cases, extend, stretch, and separate. From this pressure contraposition and as a consequence of the retreat and wrinkling of the Continental Plate, tectonic activity has influenced profoundly all of the landforms of the western two-fifths of the United States.
These geologic dynamics, over the ages, shaped the Cascade and other Pacific Coast mountain ranges, the Sierra Nevadas, the Northern and Southern Rocky Mountains, the Colorado Plateau, and the Basin and Range (desert) areas of the Southwest. These geologic forces, including faulting, volcanic activity, and erosion have influenced the shaping of all of the region's landforms and drainage systems and even a region of Southwest soils. Wallace H. Fuller says, "The southwestern United States [soils are] defined by the area.... [which] includes the plateaus, isolated mountain ranges, intermountain desert basins, and desert plains of western New Mexico, Arizona, southern and southeastern California."

The Climate of the Physiographic Southwest

The geologic evolution of the region explains and refines many of the physiographic Southwest's climatic traits. The area's predominant weather pattern--west to east--often features warm, moist air from the Pacific Ocean. However, upon encountering the various California mountain ranges, the moist air condenses and precipitates on the windward sides and the peaks of these mountains, creating a lee or east-side rain shadow. The physiographic Southwest's low hinterland desert regions, offering no cold air with which to chill and condense whatever moisture might remain in the Pacific Ocean air mass, stays dry and cloudless. Continuing to move northeastward and upon reaching the geologically uplifted regions in central Arizona, the moist air again condenses, this time falling upon the state's San Francisco Mountains or White Mountains, usually in the form of snow. Some of this moisture occasionally makes its way into the uplands of New Mexico, too.
This particular pattern characterizes the winter more than it does the summer months. From June until September, however, another system of moist air-mass movement takes place. This pattern features weather that brings moisture to the Southwest from the Gulf of Mexico by way of north-central Mexico. Essentially the same traits characterize the precipitation pattern here: moist air--mountain ranges--precipitation.
Obviously, geology has played a major role in shaping the demographics and lifestyles of the Southwest's inhabitants. Not only does the region's physiography strongly influence the area's aridity and precipitation traits, these landforms create the runoffs and rivers and alluvial soil that have made irrigation the dominant form of agriculture--and livelihood--for the region's people for so many centuries. Moreover, the geology of the Southwest has strongly influenced outsiders' interests in the region. The promise of rare and profitable metals drew the Spaniards to the area and did the most to hasten the Southwest's Anglo occupation in the nineteenth century. In this regard, the Spaniards were deeply disappointed--and the Anglos were well rewarded.
Local geological formations, it is true, strongly influence the climate of the physiographic Southwest. However, a combination of global factors also shapes the Southwest's particular climate, as is the case with most regions elsewhere on this planet. Northern hemispheric seasons and a west-to-east North American weather pattern, including winds predominantly from the west between 30 and 60 degrees north latitude, play an important part. Other global factors influencing the Southwest's climate include unique westerly dry littoral air masses together with common hemispheric marine and continental air masses. In addition, hemispheric tropical and arctic air-mass convergence patterns, the Coriolis effect, and the jet stream play important parts in shaping the region's weather patterns. It is, however, the peculiar combination and dynamic interaction of these factors that give Americas physiographic Southwest its particular and singular climatic qualities.
Of all the climatic traits associated with the physiographic Southwest, aridity is certainly the best known. Only within 105°-119° W.L. and 30°-40° N.L. can we find areas in which annual precipitation in North America averages less than eight inches annually (see maps 6 and 7). For the most part the Southwest's hydrologic cycle is more large-scale than local, more "macro" than "micro." (The geologic influence on the region's climate is considered to be "micro" here.) While some local evaporation, convection, and condensation do figure into the summertime precipitation pattern, in general they do not play a dominant role. The moist air masses that make possible the area's precipitation originate hundreds or even thousands of miles away. It is interesting to note that despite the region's normal aridity and its substantial distance from an ocean, the Southwest's primary sources of precipitation are the Pacific Ocean and the Gulf of Mexico, with a small amount, it is true, from the Gulf of California, a branch of the Pacific.
The collision between warm, moist maritime air masses derived from these large water bodies and the drier and colder Southwest continental air mass, particularly at elevations over six thousand feet, creates most of the region's snowfall and rainfall, meager as those might be when compared with the more humid regions of the continent. For instance, a combination of these systems explains the quite regular "monsoon" system that moves into the Southwest from the Gulf of Mexico in mid to late summer. Moreover, in the wintertime, warm, moist air from the Pacific travels across California and, as it rises to ascend the Southwest's mountain ranges in an orographic manner it meets cold air, condenses, and falls--or, in the high country, it condenses, freezes, and falls. The Southwest has two precipitation seasons: December through January and July through August. However, most runoff from melting snow takes place in February and March.
Oftentimes a long-lasting stationary high-pressure zone off the coast of Southern California and Mexico's Baja California Norte diverts warm, moist Pacific Ocean air masses to either the north or south of the American Southwest, thus contributing to the region's lengthy periods of aridity. The dry air, in turn, lacking the ability to hold heat, contributes to both the annual and diurnal extremes in temperature, which also characterize the Southwest's particular climate. In addition, infrequent cyclonic storms in the Southwest give the region an unusually high level of seasonable weather and climate predictability, much more so than in the rest of the nation. The cyclonic tornadoes and hurricanes that occur in the various American regions east and northeast of the Southwest rarely appear here.
The American physiographic Southwest experiences a climate dominated by general weather characteristics that also explain the overall regional aridity of America west of the 100th Meridian (except for the very moist Pacific coastal belt north of San Francisco, California). However, only occasionally do the arctic air masses that strongly influence the climate of the nation's northwest and northeast quadrants drive far enough south to affect the Southwest's weather pattern directly. Meanwhile, the substantial low-pressure mid-continental air mass systems lying over the central part of North America are too far north and too far east to influence in any significant way the weather conditions of the Southwest. The mid-continental climatic system strongly affects those parts of Colorado and New Mexico east of the Rockies and the Pecos River. Here, as in the Great Plains states and other Midwestern regions, the sky is less blue and more milky, the air is less fresh and clean, and the light is less brilliant and sparkling. Thus it is apparent that like the physiographic Southwest, the climatic Southwest is bounded on the east by the 104th Meridian.
The aridity, the insolation, the temperature of the region can be measured. Statistics show that the physiographic Southwest, indeed, does have more sunshine and less precipitation than its coastal and continental neighbors. It also possesses unique thermal characteristics (see maps 8 and 9). The two major states of the United States's Southwest--Arizona and New Mexico--share a similar climatic pattern, but within these general similarities each state has its own distinct climatic features. Both are "inland" climatic regions, separated by considerable distance from the two major sources of moist air masses that bring precipitation to the continental United States: the Pacific Ocean and the Gulf of Mexico. Of the greatest local importance here, however, remains the fact that whatever warm, moist air that does eventually approach and travel across the Southwest is converted to precipitation primarily by encountering the cold air masses that lie above the region's mountains, highlands and, to a lesser degree, high plateaus. Were it not for this dramatic topography, the Southwest would be much more of a desert than it is. While some prehistoric and modern agriculture has relied on sufficient, timely, and predictable precipitation, the region's pattern of scarce rainfall has not encouraged dry farming. However, all of the region's agrarian societies have discovered that whatever benefits they might gain in precipitation by farming the higher elevations, they give up with a shorter frost-free growing season. The precipitation pattern does provide sources of moisture for riparian irrigation. Streams, together with their feeder systems, such as the San Juan, Rio Grande, Gila, and Pecos rivers, have provided irrigation water for such sedentary prehistoric culture sites as Mesa Verde, Chaco Canyon, Tyuonyi (Bandelier National Monument), Tuzigoot, Casa Grande, and Pueblo Grande, as well as the contemporary northern Rio Grande Valley Indian Pueblos. Prehistoric Indians and, later, the modem Pueblo Indians, Hispanos, and, still later, Anglos have all gained their livelihood from these irrigable riverine locations.
This set of geologic-climatic factors explains most of the human habitation patterns in the Southwest prior to the 1870s and has had a heavy hand in affecting human life in the region even to the present. Another geologic circumstance--nonferrous mining--explains further the demographic activity and settlement in other parts of the region. Actually, only a very few small and remote Southwestern places offered these magnets for human activity. Therefore, the very limited riparian areas and mineral belts determined the social and cultural traits of this region prior to World War II. After the war, the development of air conditioning, particularly for homes and automobiles, and a rapidly growing American affluence that enabled hordes of tourists, "snow birds," retirees, and other immigrants from throughout the nation to come to the area, the Southwest's population soared. Yet the region's general aridity and brilliant, clear air, as well as the high temperatures found in its low deserts remain some of the Southwest's most recognizable--and desirable--traits, particularly in the age of interstate freeways, air conditioning, and affluent retirees and tourists. But the smoke, smog, pollens, dust, and other refuse of prosperity, with little opposition, gradually are gaining in the environmental single-winner sweepstakes race of the region. The Southwest's numerous basins, in particular, with their pollutant-entrapping physiography and natural inversion layers, are very vulnerable to environmental air-quality decay.
At least four geographical factors enable Arizona to enjoy a watershed condition more generous to the state than is the one found in New Mexico: a closer proximity to the Pacific Ocean than New Mexico has; a central mountainous area conducive to both orographic and convection precipitation; a more favorable location and elevation in terms of the warm, moist air masses that originate over the Gulf of Mexico; and an interstate river drainage system with characteristics that happen to be extremely useful for commercial agriculture as well as for flood control, water storage, recreation, and hydroelectric power generation.
Among the climatic source regions of air masses that influence Southwestern climate are the so-called continental polar, Pacific maritime polar, Pacific maritime tropical, Gulf of Mexico maritime tropical, and tropical continental. Together, the geology and climate of Arizona and New Mexico, as well as that of Southern California, extreme southern Nevada, southern Utah, southern Colorado, and the Mexican states of Sonora and Chihuahua, create a physical geography unique to North America, and very nearly unique upon this globe. By forming outcroppings and catchment basins as well as influencing precipitation and temperature patterns, the region's particular landforms and their consequent climatic conditions shape the Southwest's economic characteristics and demographic traits. Precipitation, freezing temperatures, wind, and other erosion factors of this region help to establish and support, among other things, river systems, underground water aquifers, rich alluvial soils, and mineral outcroppings. In turn, these physical features help to explain the human activity, both prehistoric and historic, that characterizes the region.
Although unique, the climatic Southwest appears to be less well circumscribed than is the physiographic Southwest. A sharp border--the 104th Meridian--does distinguish the western margin of the Great Plains, and there does seem to be a clear "core" of Southwest insolation, temperature, and precipitation statistics. But many of these features can be found extending into much of Nevada and Utah as well as into the Mexican states of Sonora and Baja California Norte. Certain Southwest climatic traits can also be found in the Rio Grande region of southwest Texas and the eastern part of Chihuahua, Mexico.
If one superimposes the various climatic data of the region, however, a center of intensification of Southwest climatic traits can be identified. This center, at 33° N.L. and 114° W.L., a point about forty miles northeast of Yuma, Arizona, marks the heart of several broadly acceptable Southwestern climatic qualities, having the highest mean total hours of sunshine, both monthly and annually; the highest percentage of possible sunshine, monthly and annually; the highest mean daily solar radiation, monthly and annually; the highest normal daily maximum temperature for one month (July); and the largest area in North America in which there is less than twelve inches of precipitation annually. As the radius from the region's climatic center expands, the intensity of the various traits deteriorates unequally. However, the intensity of each of the various traits is very pronounced within 104°-117°W.L. and 29°-38°N.L., and so establishes boundaries which seem appropriate enough to use as delineations to encompass the "climatic Southwest." Overall, both the physiographic and climatic Southwest are rather sharply defined--and they are strikingly similar.
Biologists have identified their Southwest, too. Botanist Francis H. Elmore delineates an area roughly within the physiographic Southwest but shifted about one hundred miles to the east to encompass less of California and more of New Mexico, while Natt N. Dodge includes the Great Basin Desert, the Mojave Desert, Sonoran Desert, and the Chihuahuan Desert in his book Flowen of the Soutbwest Deserts. In Reptiles and Ampbibians of the American Southwest, M. M. Heymann finds the region, except for a bit of far western Texas, to be located entirely within the physiographic Southwest (see map 10).

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