Historical Marker Program

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100th Meridian Oklahoma/Texas State Line

Harmon County
Location: on US-62, four miles west of Hollis
Coordinates: 34.681614, -100.000335
Material: Granite
Sponsor(s): 100th Meridian Chapter Daughters of the American Revolution
Topics: Early Statehood, 1907–1941; Government; Westward Expansion, 1803–1861

The Adams-Onís Treaty (1819) designated the 100th Meridian as the boundary between the United States and New Spain (Spanish Mexico). The location of the 100th Meridian remained under dispute after the admission of Texas into the Union in 1845. In 1927, the US Supreme Court confirmed the 100th Meridian as the Oklahoma-Texas border and assigned engineer Samuel S. Gannett to locate and mark the state line.