When is an error not an error?

In the western USA wilderness, just off Route 160, stands the Four Corners Monument. It marks the spot where four states – Utah, Colorado, New Mexico and Arizona – meet. Tourists have been visiting the spot for more than one hundred years so that they can straddle the boundaries.

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There have been claims that the monument is actually two and a half miles (4km) too far west. The north-south boundary between the states is at 109 degrees 03 minutes West, and people apparently assumed that the intention was that it should be at exactly 109° W. This seems to have arisen because Congress determined that the north-south line should be at the 32nd meridian of longitude west of the meridian that runs through Washington DC, which is at 77° 03′.

Four Corners Monument
The Four Corners Monument marks the spot where Utah, Colorado, New Mexico and Arizona meet

The US National Geodetic Survey (NGS) issued a statement in 2009 explaining why the Four Corners monument is in exactly the right place. The surveyor given the job of determining the boundaries in 1875 did get it slightly wrong – it’s actually about 1800 feet (548m) east of where it was intended to be – but, given the information and technology he had, the NGS is satisfied it’s in the right place.

What’s more, they say, “A basic tenet of boundary surveying is that once a monument has been established and accepted by the parties involved (in the case of the Four Corners monument, the parties were the four territories and the U.S. Congress), the location of the physical monument is the ultimate authority in delineating a boundary. Issues of legality trump scientific details, and the intended location of the point becomes secondary information. In surveying, monuments rule!”

More detail at Why the Four Corners Monument is in Exactly the Right Place