Four Corners Monument
The Four Corners Monument marks the quadripoint in the Southwestern United States where the states of Arizona, Colorado, New Mexico, and Utah meet. It is the only point in the United States shared by four states, leading to the area being named the Four Corners region. The monument also marks the boundary between two semi-autonomous Native American governments, the Navajo Nation, which maintains the monument as a tourist attraction, and the Ute Mountain Ute Tribe Reservation.
Conjecture
In mathematics, the four color theorem, or the four color map theorem, states that, given any separation of a plane into contiguous regions, producing a figure called a "map", no more than four colors are required to color the regions of the map so that no two adjacent regions have the same color. Two regions are called "adjacent" if they share a common boundary that is not a corner, where corners are the points shared by three or more regions. For example, in the map of the United States of America, Utah and Arizona are adjacent, but Utah and New Mexico, which only share a point that also belongs to Arizona and Colorado, are not.