 The origins of the state boundaries marked by the monument occurred just prior to , and during , the American Civil War , when the United States Congress acted to form governments in the area to combat the spread of slavery to the region . When the early territories were formed , their boundaries were designated along meridian and parallel lines . Beginning in the 1860s , these lines were surveyed and marked . These early surveys included some errors , but even so , the markers placed became the legal boundaries , superseding the written descriptions of geographical meridians and parallels . This includes the Four Corners Monument , which has been legally established as the corner of the four states . 
