The only spot where four US states meet isn't quite where it's supposed to be

Arizona, Utah, Colorado and New Mexico converge at the Four Corners Monument, the only quadripoint in the United States. Modern GPS surveys show the true 37th parallel/109th meridian intersection sits about 1,807 feet, or roughly 550 metres, from the historic marker. Because 19th-century government surveys legally define boundaries once set, the marker itself, not the mathematically correct point, officially marks the state lines.

— National Geodetic Survey, NOAA, Why the Four Corners Monument Is in Exactly the Right Place — NGS Information Series