Two Arizonas, The Sonoran Desert and the Colorado Plateau

Most visitors think of Arizona as one thing: desert. They are half right.

Arizona contains two of the continent's major geological and ecological provinces, and they are dramatically different from each other. The line between them runs roughly east-west through the center of the state, marked by the Mogollon Rim, a two-hundred-mile escarpment of limestone and sandstone, capped in places by basalt that drops nearly two thousand feet in some places. Below the Rim is the Sonoran Desert. Above it is the Colorado Plateau.

The Sonoran Desert is among the hottest deserts in North America. It is also, paradoxically, home to more plant species than any other desert in the world. It covers about a hundred thousand square miles across southern Arizona, southeastern California, and northwestern Mexico. Its defining feature, the saguaro cactus, grows nowhere else on earth except the Sonoran, and even there only in certain elevations. The desert gets two rain seasons, a gentle winter rain and a furious summer monsoon that arrives in July and transforms the landscape in hours.

The Colorado Plateau is something else entirely. It occupies the northeastern quarter of Arizona at elevations between five thousand and eight thousand feet. It is a country of red rock canyons, painted mesas, petrified forest, volcanic cinder cones, and ponderosa pine forests. The Grand Canyon is the most famous feature carved into it, but there are dozens of others: Canyon de Chelly, Monument Valley, the Painted Desert, Petrified Forest.

Two ecosystems, two histories, two Arizonas layered into one state. You cross from one to the other somewhere around the Rim, the exact line varies by the direction you're traveling and the season you've picked, and the land changes before your eyes.