In 1852, Randolph B. Marcy, a captain in the U.S. Fifth Infantry, and George B. McClellan led a company into the Texas panhandle to determine the locations of the headwaters of the Red River. That summer, the team discovered two main branches of the Upper Red River that intersect the 100th Meridian, with the North Branch southeast of Pampa. Earlier treaties had used the Red River as a boundary, but it had been unclear which fork was meant when the boundary was first defined. In 1896, the South Branch was determined to be the main stream and the boundary between Texas and Oklahoma.