Arizona | Geography, Facts, Map, & History (2024)

Relief

To Arizona’s two major physiographic divisions, the Colorado Plateau and the Basin and Range Province, geologists add the Transition Zone (or Central Highlands). The northeastern two-fifths of Arizona is part of the scenic Colorado Plateau. Far less rugged than adjacent portions of the plateau in Utah, these tablelands in Arizona consist mainly of plains interrupted by steplike escarpments. Although they are labeled mesas and plateaus, their ruggedness and inaccessibility have been exaggerated. The incomparable Grand Canyon of the Colorado River provides the major exception to what has proved to be an area easily traversed. Forest-clad volcanic mountains atop the plateaus provide the state’s highest points: Humphreys Peak, 12,633 feet (3,851 metres), in the San Francisco Mountains, and Baldy Mountain, 11,403 feet (3,476 metres), in the White Mountains.

More than 200 miles (320 km) of the southern border of the Colorado Plateau is marked by a series of giant escarpments known collectively as the Mogollon Rim. West and south of the rim, a number of streams follow narrow canyons or broad valleys south through the Transition Zone and into the Basin and Range Province. The Transition Zone bordering the plateaus comprises separated plateau blocks, rugged peaks, and isolated rolling uplands so forbidding that they remained mostly unexplored until the late 19th century. The zone marks the ecological border between the low deserts and the forested highlands; it combines elements of both with, for example, the Spanish bayonet of the Sonoran Desert growing alongside the juniper characteristic of higher elevations.

The Basin and Range region of the southern and western third of the state contains the bulk of the population but none of the large canyons and mesas for which Arizona is famous. It consists largely of broad, open-ended basins or valleys of gentle slope. Isolated northwest-to-southeast–tending mountain ranges rise like islands in the desert plain.

Contrary to desert stereotypes, sand dunes are nearly nonexistent, and stony desert surfaces are seldom visible except in the far southwestern portion of the state. The younger soils of river floodplains provide the more-desirable soils for agriculture.

Drainage

Virtually all of Arizona lies within the Colorado River drainage system. The Gila River, with its major feeder streams—the Salt and the Verde—is by far the Colorado’s main Arizona tributary.

The Black, White, and Verde rivers are the primary perennial tributaries of the Salt River, which enters the Gila River southwest of Phoenix. Only during the infrequent—and occasionally devastating—flood periods does runoff water advance downstream past the numerous dams built on the Salt’s system. The Gila River rises in that part of the Mogollon Rim located in western New Mexico, and it includes another and smaller Mogollon Rim tributary, the San Francisco River. Two intermittent southern Arizona streams, the Santa Cruz and San Pedro rivers, flow northward into the Gila, while two other intermittent streams, the Agua Fria and Hassayampa rivers, drain central Arizona southward into the Gila. Dams and irrigation systems, except on rare occasions, leave the Gila River dry for most of its length.

The Little Colorado River—which drains the Mogollon Rim’s lee side and flows from southeast to northwest into the Colorado River between Marble Canyon and the Grand Canyon—draws and transports little water from its large watershed. Because of the rain shadow effect on the Mogollon Rim’s lee side, the Little Colorado usually is no more than a trickle and often is dry. Several other small and intermittent streams, such as the Bill Williams River, drain a large but arid part of western Arizona.