The Gadsden Purchase Treaty was signed on December 30, 1853 and finalized in 1854.
The land purchased covered southern Arizona south of the Gila River and the southwest corner of New Mexico. The land consisted of 29,640 square miles. Purchase price was $10 million. The cost per acre was about 53 cents.
The specific location, according to History of Arizona, is "from a point on the Rio Grande at latitude 31 degrees, 47 min. North and continued 100 miles due west; then south to lat. 31 degrees 31 min. North; then due west again to 111th meridian, 20 English miles below its junction with the Gila, then up the Colorado to the former line to the Pacific Coast."
Sloan, Richard E. and Ward Adams. History of Arizona, opens a new window. v.1, Page 157.
"Ganga deal: 53 (cents)/ acre." Tucson Citizen. December 29, 2003 Page C1.
Gadsden Purchase, 1853-1854, opens a new window | U.S. Department of State, Office of the Historian
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