In the early spring, especially after a rainy winter, the desert bajadas and valleys bloom with color as dormant wildflowers burst back to life. Various shades of photogenic whites, yellows, blues, reds, and purples contrast with the uniform rich green of the well-watered springtime desert to create a truly beautiful but ephemeral scenery.
Some of the most common bloomers are the light-purple Arizona Lupine, the deep-yellow Mexican Goldpoppy, the dark-pink Parry Pestemon, and the virginal-white Desert Lily. In summer the northland meadows and grasslands bloom with wild color as well.
Below 3,500 feet or so, the Lower Sonoran Life Zone predominates, characterized by creosote, palo verde, and mesquite trees on the plains and thick stands of various cacti and other dry-adapted plants on the slopes and bajadas. Arizona is the only state where three major deserts converge: The Sonoran stretches across the southern portion of the state and includes the Phoenix and Tucson  areas, while the Mojave dominates on the western reaches. The Chihuahuan Desert of Mexico stretches north into southeastern Arizona.
Between 4,500 and about 7,000 feet you’re in the Upper Sonoran Life Zone, characterized by scrub oak, piñon pine, juniper, manzanita, and sagebrush grasslands; this zone is often called the chaparral. The midlands of the state, at around 6,000 feet and higher, are marked by the transition zone, and this is where you start to see the beginnings of the vast ponderosa pine forests. Above 8,500 feet or so thick stands of evergreen conifers and white aspen are common. Above 9,500 feet or so, a height reached in Arizona primarily by climbing up towering mountains, the Subalpine Zone has tough Engelmann spruce and bristlecone pine, and above that it’s all barren rocks and tundra.
The official Arizona state tree is the palo verde, a green-skinned desert dweller that can grow up to 25 feet high. The tree proliferates throughout the Lower Sonoran Life Zone and is often a close neighbor to the saguaro, the baby buds of which use the palo verde’s cover to hide and grow. Other common desert trees are the ubiquitous mesquite, which has often been used for firewood and building, and its beans have nourished people and animals alike. Both the mesquite and the palo verde bloom yellow in the spring.
Ironwood trees and drought-resistant evergreens grow along slopes and washes in the desert. Bushy plants crowd the desert as well; creosote is everywhere, as is prickly catclaw and rabbitbrush, all of which bloom yellow. Adding a little red to the bloom time is the ocotillo, which is everywhere in the desert and resembles a sprouting group of pipe cleaners. Throughout the desert and into the chaparral of the transition zones you’ll see several species of agave, an important plant to the human population in that it can be turned into mescal and tequila. The Agave parryi, or century plant, blooms only once, with a tall stalk of yellow flowers, before dying.
In the scrublands and chaparral and higher you’ll see scrub oak, piñon pine, juniper, manzanita, and other brushy trees. In the high country, above 6,000 feet or so, you’ll see ponderosa pine mainly. Higher still, in the montane forests at the highest elevations, fir, spruce and aspen forests dominate. Along many waterways, called riparian areas, are big cottonwoods and willows and sycamores.