Arizona

I

Introduction

Arizona, state in the southwestern United States. It is a land of seemingly limitless space and tremendous vistas. Arizona was the last of the 48 adjoining continental states to enter the Union. From its admission on February 14, 1912, until the admission of Alaska and Hawaii in 1959, it was the youngest state.

Arizona’s landscape is one of great diversity. Sun-swept mountains and valleys, lofty plateaus, narrow canyons, and awesome stretches of desert make it one of the most beautiful states in the nation. This scenic beauty, coupled with an ideal climate, has made Arizona very popular with tourists.

Imperial Spain and, later, independent Mexico once controlled this land, and there the Native American, Spanish, and Anglo-American cultures met and fused. Although most of the Native Americans now live on reservations and Mexico and Spain long ago relinquished control of the area, traces of Arizona’s past still remain. The Native American culture has been preserved on the reservations, and Mexican and Spanish influences may be seen in architectural styles and place-names.

Arizona has undergone great changes since the 19th century, when it was a rough-and-tumble mining and cattle territory. Although it still retains much of the character of the old West for tourists, it is a modern urban and industrial state, with large cities, highly mechanized farms, and rapidly expanding industries. Phoenix is the center of Arizona’s largest urban area and the state’s capital.

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The name of the state is derived from the Native American word arizonac believed to mean “place of the small spring.” Arizona is popularly known as the Grand Canyon State, after its most remarkable physical feature, the Grand Canyon of the Colorado River.

II

Physical Geography

Arizona ranks sixth among the states in size. With an area of 295,253 sq km (113,998 sq mi), including 943 sq km (364 sq mi) of inland water, it is almost as large as all of the New England states and New York combined. Arizona’s mean elevation is about 1,250 m (4,100 ft). Roughly rectangular in shape, the state’s extreme dimensions are 631 km (392 mi) from north to south and 549 km (341 mi) from east to west. Most of the western border is formed by the Colorado River. The northeastern corner is the only place where four states meet: Arizona, New Mexico, Colorado, and Utah.

A

Natural Regions

All of Arizona lies in the Intermontane Plateaus, which form one of the major physiographic divisions of the United States. The state can be divided into three physiographic regions: the Colorado Plateau, the Basin and Range region, and the Transition Zone, or Central Highlands.

The Colorado Plateau is a flat, dry, semidesert region that covers the northern two-fifths of the state. Many rivers have carved deep canyons into this region, with the most famous example being the Grand Canyon of the Colorado River. The river in the Grand Canyon is as much as 1,500 m (5,000 ft) below the level of the surrounding plateau. Canyon de Chelly and Oak Creek Canyon are also beautiful, but lesser known, canyons carved into the plateau by tributaries of the Colorado River.

About 2 billion years ago this area, now mostly 1,500 to 2,400 m (5,000 to 8,000 ft) above sea level, lay under a vast sea. Through the ages the land emerged and resubmerged repeatedly, and many different rock types, including igneous, sedimentary, and metamorphic, formed. Rivers cut through layers of soil and rock to reach the ancient granites, quartzites, and rocks now revealed. Water and wind have eroded the edges of canyons and the surface of the plateaus, carving isolated, steep-sided, flat-topped hills called mesas. Underlying rocks such as sandstones, shales, and limestones have also been exposed by erosion, creating a kaleidoscope of brilliant colors on canyon and mesa walls.

North of the Grand Canyon is the Kaibab Plateau, which is an area extending from Utah into Arizona. The Kaibab Plateau resembles a peninsula.

The section of the Colorado Plateau located in the northern and northeastern part of the state is a maze of valleys and mesas. Carved knobs, rounded domes, and tall rock spires that pierce broad valleys earned the area its name of Monument Valley. The Painted Desert, where red, yellow, purple, blue, brown, and gray rocks alternate in a vivid display of colors, extends south from the Grand Canyon to the Mogollon Rim. Within the Painted Desert is the Petrified Forest National Park, an area of giant, ancient fallen trees that slowly petrified over thousands of years.

South of the Grand Canyon lies the San Francisco Plateau, which is covered by ancient lava flows and dotted with extinct volcanic cones such as Humphreys Peak, 3,851 m (12,633 ft) tall, the highest point in Arizona. The southeastern part of the Colorado Plateau in Arizona is part of the Datil section, noted for its solidified lava flows and other volcanic features. The southern border of the Colorado Plateau is distinguished by an extensive volcanic escarpment known as the Mogollon Rim. The Rim, which extends from central Arizona toward the southeast and terminates in the Mogollon Mountains, was originally created by tectonic pressure, uplift of the plateau, and, most important, erosion of the Transition Zone. The steep rock wall reaches about 600 m (about 2,000 ft) high in some places. To the south of the Mogollon Rim is a narrow strip of land known as the Transition Zone.

The Transition Zone is characterized by mountain ranges so close together that the area appears as a cluster of rugged peaks separated by steep, narrow valleys. The Mazatzal, Santa Maria, Sierra Ancha, and White mountain ranges are found in this zone, which occupies part of the area once known as the Central Highlands. So uninviting was the landscape that prospectors did not explore the region until the late 19th century. Since then, more than 90 percent of Arizona’s mining activity has taken place in this area.

The Basin and Range region, known to Arizona residents as the Sonoran Desert, occupies most of the southern part of Arizona. It is composed of a series of smooth-floored desert basins separated by mountain ranges that extend from northwest to southeast. Mountains in this region include the Chiricahua, Gila, Pinaleno, Huachuca, Hualapai, Santa Catalina, Santa Rita and Superstition ranges. The portion of the Basin and Range region that lies to the south and west is a low, dry landscape. Elevations in this area range from as low as 43 m (141 ft) at Yuma to 3,267 m (10,717 ft) atop Mount Graham. While the land has little rain, along the western border of Arizona farms irrigated with waters from the Colorado River produce abundant crops. Most of the loose material on the mountains in this region has been carried down by infrequent but violent cloudbursts to form thick fans of sand and gravel where the steep slopes meet the basin floor. When irrigated, this area produces excellent crops. Also, the state’s largest cities are located in this region. Most elevations in the Basin and Range region are from 150 to 1,500 m (500 to 5,000 ft), but some mountains rise to more than 3,400 m (11,000 ft). The region is generally higher in the east than in the west. Its desert plains are drained by the lower courses of the Colorado and Gila rivers.

B

Rivers and Lakes

The most important river in Arizona is the Colorado, which enters the state in the north, flows southwestward to the state’s western boundary, and then follows the boundary south into Mexico. In the Colorado Plateau, its main course is joined by the Little Colorado, which runs from south to north. Because of the rain-shadow effect of the Mogollon Rim, the Little Colorado draws very little water from a relatively large watershed, usually containing a mere trickle of water in its riverbed. The Colorado River’s principal tributary is the Gila River, which flows all the way across the southern part of the state from New Mexico to the California border. From the mountains and plateaus of central Arizona, the Gila River receives the Salt, Agua Fria, and Hassayampa rivers. The Salt River is itself fed by the Verde River. The Gila River also is joined by rivers draining the Mogollon Rim and other mountains in the Central Highlands, as well as mountain ranges such as the Sierriata and Santa Catalinas in the southern part of the state. Heavy rainfalls typical in the summer months over the Mogollon Rim drain into the Black, White, and Verde rivers. In February, March, and April melting snow from the same regions occasionally creates flood conditions along the Salt River and around Phoenix. These three rivers are important tributaries to the Salt River, which is a primary source of water for the highly-populated Phoenix metropolitan and surrounding agrarian areas. The Santa Cruz and San Pedro rivers flow northward out of southern mountain ranges near the Mexican border and feed into the Gila River as well.

Very few of Arizona’s rivers have a year-round steady flow. During rains many rivers fill with rushing water, while at other times of the year they appear dry. However, water is often flowing beneath the sandy riverbeds. None of those rivers is now used for navigation, but during the second half of the 19th century steamboats regularly came up the Colorado as far as about 300 km (about 200 mi) beyond Yuma.

Eleven dams control run-off from the Mogollon Rim, creating the state’s largest lakes. Arizona has few natural lakes, and those that do exist are small. Enormous lakes have formed behind dams built for flood control, irrigation, and power development on major rivers such as the Verde, Agua Fria, Salt, and Gila. The largest lake is Lake Mead, with an area of 603 sq km (233 sq mi), formed by the Hoover Dam on the Colorado River. It lies partly in Arizona and partly in Nevada and backs into the lower portion of the Grand Canyon. Other large lakes created by dams include Theodore Roosevelt Lake, behind the Roosevelt Dam on Salt River; San Carlos Lake, behind the Coolidge Dam on the Gila River; Lake Havasu, behind the Parker Dam on the Colorado River; and Lake Powell, which is partly in Utah and formed behind the Glen Canyon Dam on the Colorado River.

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