There is a very good series on the History Channel on how the states of the United States got their shape. Unlike in the east, in the west, the borderlines we drawn in Washington, DC, after the various territories were obtained by the US. There was a process. Four Corners is a result of this process.

Four Corners lies on Navajo land. The monument at this location is maintained by the Navajo. Even though it has become a tourist destination of sorts, it is, unfortunately, not that well maintained. It is just off US Route 160.

https://en.wikipedia.org/wiki/Four_Corners