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.