International Boundary Marker is located in Texas

The International Boundary Marker, also known as the Republic of Texas Granite Marker, is a boundary marker located on the Louisiana-Texas border near the junction of Texas State Highway 31 and Louisiana Highway 765, southeast of Deadwood, Texas. The marker was created in 1840 and placed in 1841 to mark the international border between the United States and the Republic of Texas. The survey which established this border lasted from May 1840 to June 1841; the survey team faced hazardous, swampy conditions in their work and were forced to take several extended breaks due to weather and a lack of funding. The boundary marker is the only marker remaining from the Texas border survey and is the only known international boundary marker located entirely within the United States.

• http://en.wikipedia.org/wiki/International Boundary Marker