Quadripoint
The Four Corners Monument is the only point in the United States where four states meet: Colorado, Utah, New Mexico, and Arizona meet at right angles. The United States first acquired the area now called Four Corners from Mexico after the Mexican–American War in 1848. In 1863 Congress created Arizona Territory from the western part of New Mexico Territory. The boundary was defined as a line running due south from the southwest corner of Colorado Territory, which had been created in 1861. By defining one boundary as starting at the corner of another Congress ensured the eventual creation of four states meeting at a point, regardless of the inevitable errors of boundary surveying. The monument is centered at .
Article Four of the United States Constitution
The First Clause of Section Three, also known as the Admissions Clause, grants to Congress the authority to admit new states into the Union. Since the establishment of the United States in 1776, the number of states has expanded from the original 13 to 50. It also forbids the creation of new states from parts of existing states without the consent of the affected states and Congress. This latter provision was designed to give Eastern states that still had claims to Western lands (e.g., Virginia and North Carolina) to have a veto over whether their western counties (which eventually became Kentucky and Tennessee) could become states. It would later be applied with regard to the formation of Maine (from Massachusetts) and West Virginia (from Virginia).