In 1853, the united states paid mexico $10 million for the southwestern part of new mexico and the area in arizona south of the gila river in a deal known as the gadsden purchase. why did the united states want this piece of land? a. the area was heavily populated with many thriving cities. b. they wanted to build a railroad route through the area. c. they thought there were vast deposits of gold in the area. d. there were deep water ports with access to the pacific ocean.