Sonora, officially Estado Libre y Soberano de Sonora (English: Free and Sovereign State of Sonora), is one of the 31 states which, along with Mexico City, comprise the Federal Entities of Mexico. It is divided into 72 municipalities; the capital city is Hermosillo. Sonora is bordered by the states of Chihuahua to the east, Baja California to the northwest and Sinaloa to the south. To the north, it shares the U.S.–Mexico border primarily with the state of Arizona with a small length with New Mexico, and on the west has a significant share of the coastline of the Gulf of California.

Sonora's natural geography is divided into three parts: the Sierra Madre Occidental in the east of the state; plains and rolling hills in the center; and the coast on the Gulf of California. It is primarily arid or semiarid deserts and grasslands, with only the highest elevations having sufficient rainfall to support other types of vegetation.

Sonora is home to eight indigenous peoples, including the Mayo, the O’odham, the Yaqui, and Seri. The state has been economically important for its agriculture, livestock (especially beef), and mining since the colonial period, and for its status as a border state since the Mexican–American War. With the Gadsden Purchase, Sonora lost more than a quarter of its territory. From the 20th century to the present, industry, tourism, and agribusiness have dominated the economy, attracting migration from other parts of Mexico.

The Border

Sonora's border with the United States is 365 miles long, and runs through desert and mountains, from the western Chihuahuan Desert, through an area of grasslands and oak mountain areas to the Sonoran Desert west of Nogales. The area gets drier from here west and the last third of the border is generally uninhabited. There are six official border crossings. From east to west these at Agua Prieta, Naco, Nogales, Sasabe, Sonoyta and San Luis Río Colorado. In populated areas, much of the border is marked by corrugated metal walls, but most of the rest is marked by barbed wire fence and border monuments.

Like others in the world, the border is a culture unto itself, not belonging 100% to either country. Interaction between the peoples on both sides is a part of both the culture and the economy. In the 1980s, an international volleyball game was regularly held near Naco, with the chain link border fence serving as the net. Much of Arizona and Sonora share a cuisine based on the wheat, cheese and beef that was introduced to the region by the Spaniards, with wheat tortillas being especially large on both sides of the border. This diet is reinforced by the vaquero/cowboy tradition which continues in both states. The six border crossings are essential to the existence and extent of the communities that surround them, as most of them function as ports for the passage of goods between the two countries. People regularly shop and work on the other side, taking advantage of opportunities there. The economic opportunities of the border are not equal on both sides. Most of the population along this border lives on the Sonoran side, many of which have moved here for the opportunities created by the maquiladoras and other businesses. These are lacking on the Arizona side.

The border has separated the region's indigenous populations, such as the Tohono O’odham. While members of the Tohono O’odham have special border crossing privileges, these have become endangered as Mexican farmers encroach on tribal lands in Sonora, which are vulnerable to drug smugglers. Yaquis in Arizona travel south to the Yaqui River area for festivals, especially Holy Week, and Yaquis travel north to Arizona for cultural reasons as well. When Father Kino arrived in this area, he named much of it the Pimería Alta, as Pima territory extends from the highlands of eastern Sonora up towards Tucson.

Authorities on each side work to keep out from the other that which is undesirable. For the United States, this mostly involves drugs and illegal immigrants. For Mexico, this mostly involves struggling against the importation of untaxed goods, especially automobiles. Smuggling people and drugs into the United States is big business in Mexico, but while it affects everyone living on the border, it is generally not seen, except for occasional newspaper headlines, occasional violent crime and religious articles geared to those in the trade. Illegal crossings taking place through tunnels, hidden cars and trucks or most commonly, simply passing through a gap in the fence, especially in the more remote areas. In 1990, a tunnel linking two warehouses in Agua Prieta and Douglas, AZ was discovered. It was sophisticated with hydraulic equipment and means to move large quantities of goods. At least three corridos have been written about this tunnel.