United States Geological Survey

Ever wondered how Arizona’s southern border got its shape? Why, for instance, doesn’t the state line go straight across? Why is the border on an extreme slant? At least one answer may lie in a group of land surveyors who worked the area in the days before statehood and, more specifically, about what they’d been drinking when they drew the line.

When it comes to the Arizona state line, historians say there’s an old wive’s tale that goes something like this: The land surveyors, who were in Nogales at the time, were looking for a drink and found that the closest bar was in Yuma. While making the trip, they actually marked the state line. But, did you know the slanted borderline was really a decision made by the U.S. and Mexico?

“Instead of being a story of great intrigue and excitement,” said John Southard, an Arizona historian. “When you boil it down, its simplest form, it’s a real estate transaction.”

Southard said after the Mexican-American War, the U.S. acquired many Southwestern states from Mexico, including Arizona. At the time, Arizona was bordered by the Gila River on the south and the U.S. wanted to claim more territory by extending it further.

U.S. Ambassador to Mexico James Gadsden negotiated the purchase of land further into Mexico. He came up with several proposals, most including what the U.S. government had in mind.

“There was a proposal to extend U.S. territory down to Guaymas, which is a port on the Gulf of California," Southard said. "It was actually held by the Americans during the Mexican-American War for a brief period.”

John Larsen Southard This D.C. Daily Evening Star article from Jan. 27th, 1854, “The New Treaty with Mexico,” shows that even the DC press was foggy on the details of exactly what the United States was to gain.

Southard said Mexico’s Baja California was also part of the original plan. The U.S. saw this as a way to ensure greater access to commerce.

Not wanting to divide its territories of Baja California and its main land, the Mexican government refused the plan. The U.S. wasn’t sure this plan would be ideal either. There was a contentious issue clouding the country at the time, the debate over expanding the reach of legalized slavery for growing crops, such as cotton.

“Abolitionists and other opposed to the expansion of slave-holding territory objected to the idea of obtaining such a large swath of land and particularly a port that could increase the trade possibilities for cotton growers and other slave holders," Southard said.

Tensions were still high after the Mexican-American War. And the U.S. and Mexico were afraid of further dividing their respective countries, so the two sides agreed upon a simpler Arizona-Mexico border, the one we have today. Ultimately, the U.S. acquired the land needed for an all-weather transcontinental railroad.

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