Why the Four Corners Monument is in Exactly the Right Place (2024)

Friday, May 15th, 2009

Why the Four Corners Monument is in Exactly the Right Place

Recent media reportsincorrectly stated that the location of the Four Corners survey monument –marking the point common to Arizona, Colorado, New Mexico, and Utah – is inerror by 2.5 miles and suggested that the monument therefore does not correctlymark the intersection of the four states. These reports also erroneouslyattributed the discovery of this supposed error to the National Oceanic and AtmosphericAdministration’s (NOAA) National Geodetic Survey (NGS). NGS did not, in fact,make any claim or pronouncement that the monument is incorrectly located orsuggest that it should be relocated. NGS has, however, worked with the mediato correct inaccuracies in the initial reports, clarifying that the distancebetween the actual location of the monument and its intended location issubstantially less than the reported 2.5 miles, and that – as affirmed by theBureau of Land Management (BLM) – it does indeed correctly mark the four-state-intersectionpoint. Because NGS was specifically named in the reports, this brief document wasprepared to present some pertinent facts and history about the Four Cornersmonument and its placement.

In 1875, a surveyornamed Chandler Robbins was contracted by the U.S. General Land Office (GLO),the BLM’s predecessor, to survey the entire boundary between the territories ofArizona and New Mexico, from the U.S.-Mexico boundary to the 37^thparallel of latitude north of the equator. He was charged with also establishing,at the boundary’s northern terminus, the Four Corners monument, as it would beknown upon completion of the other territorial boundary surveys terminating there. Robbins was directed to base his survey on the geographic coordinates of ShipRock (a prominent northwestern New Mexico landform), which had been determinedthe previous year during the decade-long U. S. Geographical Surveys West of the100^th Meridian, led by First Lieutenant George Wheeler.

An 1863 Act of Congress,signed by President Lincoln, which separated Arizona from New Mexico, specifiedthat the dividing boundary should be coincident with the 32^nd meridianof longitude west of the Washington (DC) Meridian. The Washington Meridian,which had been in use since 1850, was defined as bisecting the dome of the oldNaval Observatory, situated at a longitude of 77 degrees 03 minutes West (forsimplicity, longitude values presented here are rounded to the nearest arcminute). In fact, the boundaries of 11 western states are similarly longitude-referencedto the Washington Meridian, and not the Greenwich Meridian. This practice wasin place in the U.S. until 1912, when our nation adopted Greenwich as itsstandard longitude reference.

Hence, what Congresshad specified for the Arizona-New Mexico boundary, and the Four Cornersmonument, was that they should be established at a longitude of 109 degrees 03 minutesWest, as referenced to the Greenwich Meridian. Therein, we believe, lies thesource of the invalid report of a Four Corners monument location error of 2.5miles. Some people apparently relied on the incorrect premise that the marker wasoriginally intended to be located at a longitude of exactly 109 degrees West. But,Robbins followed his marching orders correctly, and the Four Corners monumentwas established at the point he determined, to the very best of his ability andusing the available technology, to be the prescribed location of 109 degrees 03minutes West longitude and 37 degrees North latitude. There, his meridiansurvey intersected the 1868 New Mexico-Colorado boundary survey, which ranalong the 37^th parallel. Subsequent surveys established theUtah-Colorado and Arizona-Utah boundaries, thereby completing the Four Corners assemblageof territorial (eventually state) lines, as specified by Congress.

It is interesting tonote that, upon completion of his Arizona-New Mexico boundary survey, ChandlerRobbins went to the effort to write a letter to the editor of The Santa FeNew Mexican (still today’s daily newspaper) explaining the very issue of thedifference between longitude values referenced to the Greenwich Meridian andthose referenced to the Washington Meridian. In this letter of November 1, 1875,Robbins included the following explanation:

It seems to havebeen the general impression that the line was the 109 degrees of longitude westof Greenwich. Such is not the case, as the law makes it 32 degrees of longitudewest from Washington, which corresponds to 109 degrees 02 minutes 59.25 secondswest from Greenwich, and which places the line a small fraction less than threemiles farther west than would have been the case if it had been run as the 109degrees of longitude.

In these few words, Robbins takesthe mystery out of a technical issue that has evidently confused and misled somepeople for more than a century.

Nonetheless, thereremains the question of how close the Four Corners monument is relative to its intendedlocation. In fact, there is a discrepancy between the actual location, whichwe know to a high degree of accuracy, and our best knowledge of where it wasintended to be located. But, instead of a 2.5-mile discrepancy, as reported inthe initial news items, this offset is in fact only about 1800 feet, or less. Notonly is the offset only about one-tenth of the alleged location error, it is inthe opposite direction; the intended monument location is west of the actual monument. There is, however, uncertainty in precisely quantifying the relationshipbetween the intended and actual monument locations due to changes, since 1875,in some technical details of the geodetic reference systems utilized. The actualoffset might in fact be considerably less than our estimate.

Regardless of thetechnical nuances, we can confidently say that, considering the relativelyprimitive surveying technology of the day, the remote and difficult prevailing fieldconditions, and uncertainty in the survey’s beginning coordinates for Ship Rock,Chandler Robbins’ survey was a resounding success. He “nailed” the location ofthe Four Corners, to the best of his ability, using the tools and information availableto him at the time.

Finally, we cannotoveremphasize the fact that the aforementioned technical geodetic details areabsolutely moot when considering any question of the correctness or validity ofthe Four Corners monument in marking the intersection of the four states. Indeed, the monument marks the exact spot where the four states meet. Abasic tenet of boundary surveying is that once a monument has been establishedand 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 ofthe physical monument is the ultimate authority in delineating a boundary. Issues of legality trump scientific details, and the intended location of thepoint becomes secondary information. In surveying, monuments rule!

The physical monumentmarking the Four Corners has been rebuilt multiple times by the GLO and BLM overthe years since Robbins installed a seven-foot-tall sandstone shaft to mark thespot. But the same location has been perpetuated now for more than a centuryand a quarter. The current monument complex was constructed in 1992 andincludes a visitor plaza area surrounding a commemorative survey disk. TheFour Corners monument has been included in modern high-accuracy GlobalPositioning System (GPS) geodetic surveys, producing three-dimensionalcoordinates accurate to an inch or better. These survey results anddescriptive information about the monument are included in the database of geodeticcontrol points maintained by NGS. The geodetic control datasheet for the FourCorners monument (designation: CO UT AZ NM) can be found online here: http://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=AD9256.

Hence, in addition tomarking the intersection point of four states, the Four Corners monument isalso a component of what is known today as the National Spatial ReferenceSystem (NSRS), which is maintained by NGS and serves as the nation’s geospatialframework. Through its published geodetic position, the monument provides amechanism for geospatial professionals (land surveyors, engineers, etc.) toaccess this framework with a high degree of both accuracy and certainty. TheFour Corners monument continues its long-standing heritage of playing animportant role in the history and demarcation of the American West – all thewhile bearing witness as the only point of intersection of four U.S. states – inexactly the right place.

NGS is responsiblefor defining, maintaining, and providing public access to the NSRS – aconsistent national coordinate system that provides the foundation for mappingand charting; some state boundaries; transportation, communication, and landrecords systems; as well as scientific and engineering applications. Moreinformation about NGS and the various components of the NSRS can be found at: http://www.ngs.noaa.gov. NGS is notnormally involved in boundary-related issues and is providing the information containedin this document simply as a statement of clarification of the pertinent factsand background regarding the Four Corners monument. The field notes and platsfor the remonumentation of the Four Corners monument and the surveys/resurveysof the state boundary lines can be obtained from the BLM at: http://www.glorecords.blm.gov/.

 For additional information, please contact William Stone, NGS, at: william.stone@noaa.gov. 

 To listen to a podcast on this subject, click here:

 Making Waves Episode 25— April 29, 2009 (12 minutes) Where exactly is Four Corners?