The Sonoran Desert is a deceptive landscape. The soft greens and yellows can appear monotonous, yet stop and look closely and they reveal staggering variety. It rains here only rarely, yet during the summer rainy season this arid land is positively lush.

Once a year, in the spring, the land bursts with otherwise dormant wildflowers, like a one-night-only command performance. The region is dominated by desert, a flat land stretching out like a vast forgotten sea, yet increase your elevation into one of the region’s sky islands and you will be hunting for tropical birds in a misty creek bed among oak and pine, or, if you go high enough, clamping on a pair of skis.

The Sonoran desert is a much more varied desert than others in North America. Southern Arizona, of which Tucson is the largest city by far—really the only metro area of any size—is often referred to by those who study the region’s biomes, as the sky islands. The region’s “sky island” mountain ranges, some of which reach heights of 10,000 feet above sea level or more, are high, isolated mountains looking out over a sea of arid desert, and as such they support an astonishing variety of plants and animals.

It’s often said that driving from the desert floor in Tucson, at around 2,000 feet above sea level, to the top of nearby Mount Lemmon, at just above 9,000 feet—about an hour’s drive—is akin, biologically speaking, to traveling from Mexico to Canada.

The region’s mountain ranges—the Santa Catalina Mountains north of Tucson; the Santa Rita Mountains to the south, the Rincon Mountains to the east, the Huachuca Mountains to the southeast, and other ranges farther east near the New Mexico border—represent a transitional zone from the colder Rocky Mountains to the more tropical and subtropical Sierra Madre Occidental in Mexico.

The mid-ranges of the mountains are dominated by Madrean evergreen woodlands or Mexican oak-pine woodlands. Sometimes the whole region is referred to as the Madrean Archipelago. On the slopes of these mountains, called the “bajada,” scrub oak turns into desert trees, such as mesquite and palo verde, and at the base there are sometimes vast semidesert grasslands sweeping across the land.

And in the middle of all this natural diversity and beauty sits Arizona’s second-largest city, Tucson, the county seat of Pima County. It’s not always necessary to delineate the Tucson metro area from Pima County as a whole; indeed, Tucson is really the primary metropolitan hub for four counties in the southern section of Arizona—Pima County, Cochise County to the southeast, Pinal County to the northwest, and Santa Cruz County to the south.

Created in 1864 around the same time as the Territory of Arizona, Pima County has about 9,184 square miles with elevations that range from 1,200 feet to 9,157 feet on top of Mount Lemmon in the Santa Catalina range, which looms over the northern portion of Tucson and adds significantly to the dramatic, exotic look of the city. Nearly half of the land in Pima County—about 42 percent—is set aside as reservations for the Tohono O’odham, formerly called the Papago, and the Pascua Yaqui, a small tribe of indigenous people that moved north from Mexico seeking refuge from persecution in the early 20th century.

As is common in Arizona, a state created by the federal government out of a vast region gathered together under the indefinite rubric of New Mexico, only about 13 percent of the land in Pima County is privately owned. The rest, aside from the reservations, is either controlled by the state or the federal government. This, combined with the area’s diverse natural wonders, is one of the main reasons Tucson has become a favorite spot for wilderness lovers and outdoorspeople.

Pima County has a population of about a million persons, about 530,000 of which live in the city of Tucson, making the Old Pueblo the nation’s 32nd-largest city. Spread out and sprawling, Tucson comprises about 192 square miles, and sits at an elevation of 2,389 feet above sea level. The city is connected to the rest of the nation via I-10, and is connected to Mexico, just 60 miles south, by I-19.