 The area now called Four Corners was initially American Indian land and beginning in the 16th century it was claimed by Spain as part of New Spain . Following Mexico 's independence from Spain , the area was governed by Mexico until being ceded to the United States by the Treaty of Guadalupe Hidalgo in 1848 following the United States ' victory in the Mexican – American War . The first boundary which would become part of the monument was set as part of the Compromise of 1850 , which created the New Mexico Territory and Utah Territory . The border between the two territories was congressionally defined as the 37th parallel north by the 31st United States Congress . In 1861 , the 36th United States Congress transferred land previously allocated to the Utah Territory , to the newly created Colorado Territory . The Colorado Territory 's southern border would remain as the 37th parallel north , but a new border — between the Colorado and Utah Territories — was declared to be the 32nd meridian west from Washington . This line was derived from the reference used at the time , the Washington meridian . 
