What land was added to build a transcontinental railroad?The NortheastThe Gadsden PurchaseThe Louisiana TerritoryFlorida

The land that was added to build a transcontinental railroad was the Gadsden Purchase. This was a 29,670 square-mile region of present-day southern Arizona and southwestern New Mexico that the United States purchased via a treaty signed on December 30, 1853, by James Gadsden, the U.S. ambassador to Mexico at that time. The purpose of this purchase was to allow for the construction of a southern transcontinental railroad. The other territories mentioned, the Northeast, the Louisiana Territory, and Florida, were already part of the United States and did not need to be added for the construction of the railroad.