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 .
Four corners (Canada)
The establishment of Nunavut in 1999 led to the creation of Canada's only quadripoint at this location. In the legal definition of Nunavut, its border is specified as "Commencing at the intersection of 60°00'N latitude with 102°00'W longitude, being the intersection of the Manitoba, Northwest Territories and Saskatchewan borders". Since the intersection does not lie exactly at those coordinates, the laws are not perfectly clear about whether or not the Nunavut–NWT boundary, which has not been completely surveyed, is to meet the others in a quadripoint. Surveys began in 2011.