Arizona is a state in the Western United States, grouped in the Southwestern and occasionally Mountain subregions. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona shares the Four Corners region with Utah to the north, Colorado to the northeast, and New Mexico to the east; its other neighboring states are Nevada and California to the west and the Mexican states of Sonora and Baja California to the south and southwest.

Arizona is the 48th state and last of the contiguous states to be admitted to the Union, achieving statehood on February 14, 1912. Historically part of the territory of Alta California in New Spain, it became part of independent Mexico in 1821. After being defeated in the Mexican–American War, Mexico ceded much of this territory to the United States in 1848. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase.

Southern Arizona is known for its desert climate, with very hot summers and mild winters. Northern Arizona features forests of pine, Douglas fir, and spruce trees; the Colorado Plateau; mountain ranges (such as the San Francisco Mountains); as well as large, deep canyons, with much more moderate summer temperatures and significant winter snowfalls. There are ski resorts in the areas of Flagstaff, Alpine, and Tucson. In addition to the internationally known Grand Canyon National Park, which is one of the world’s seven natural wonders, there are several national forests, national parks, and national monuments.

Since the 1950s, Arizona’s population and economy have grown dramatically because of migration into the state, and now the state is a major hub of the Sun Belt. Cities such as Phoenix and Tucson have developed large, sprawling suburban areas. Many large companies, such as PetSmart and Circle K, have headquarters in the state, and Arizona is home to major universities, including the University of Arizona and Arizona State University. Traditionally, the state is politically known for national conservative figures such as Barry Goldwater and John McCain, though it voted Democratic in the 1996 presidential race and in the 2020 presidential and senatorial elections.

Arizona is home to a diverse population. About one-quarter of the state is made up of Indian reservations that serve as the home of 27 federally recognized Native American tribes, including the Navajo Nation, the largest in the state and the United States, with more than 300,000 citizens. Since the 1980s, the proportion of Hispanics in the state’s population has grown significantly owing to migration from Mexico. In terms of religion, a substantial portion of the population are followers of the Catholic Church and The Church of Jesus Christ of Latter-day Saints (Mormon).

CLIMATE

Due to its large area and variations in elevation, the state has a wide variety of localized climate conditions. In the lower elevations, the climate is primarily desert, with mild winters and extremely hot summers. Typically, from late fall to early spring, the weather is mild, averaging a minimum of 60 °F (16 °C). November through February are the coldest months, with temperatures typically ranging from 40 to 75 °F (4 to 24 °C), with occasional frosts.

About midway through February, the temperatures start to rise, with warm days, and cool, breezy nights. The summer months of June through September bring a dry heat from 90 to 120 °F (32 to 49 °C), with occasional high temperatures exceeding 125 °F (52 °C) having been observed in the desert area. Arizona’s all-time record high is 128 °F (53 °C) recorded at Lake Havasu City on June 29, 1994, and July 5, 2007; the all-time record low of −40 °F (−40 °C) was recorded at Hawley Lake on January 7, 1971.

Due to the primarily dry climate, large diurnal temperature variations occur in less-developed areas of the desert above 2,500 ft (760 m). The swings can be as large as 83 °F (46 °C) in the summer months. In the state’s urban centers, the effects of local warming result in much higher measured night-time lows than in the recent past.

Arizona has an average annual rainfall of 12.7 in (323 mm), which comes during two rainy seasons, with cold fronts coming from the Pacific Ocean during the winter and a monsoon in the summer. The monsoon season occurs toward the end of summer. In July or August, the dewpoint rises dramatically for a brief period. During this time, the air contains large amounts of water vapor. Dewpoints as high as 81 °F (27 °C) have been recorded during the Phoenix monsoon season. This hot moisture brings lightning, thunderstorms, wind, and torrential, if usually brief, downpours. These downpours often cause flash floods, which can turn deadly. In an attempt to deter drivers from crossing flooding streams, the Arizona Legislature enacted the Stupid Motorist Law. It is rare for tornadoes or hurricanes to occur in Arizona.

Arizona’s northern third is a plateau at significantly higher altitudes than the lower desert, and has an appreciably cooler climate, with cold winters and mild summers, though the climate remains semiarid to arid. Extremely cold temperatures are not unknown; cold air systems from the northern states and Canada occasionally push into the state, bringing temperatures below 0 °F (−18 °C) to the state’s northern parts.

Indicative of the variation in climate, Arizona is the state which has both the metropolitan area with the most days over 100 °F (38 °C) (Phoenix), and the metropolitan area in the lower 48 states with the most days with a low temperature below freezing.