San Juan River

The San Juan River is the largest and most important river in the Mexican state of Nuevo León. The river has a total surface area of 20,212 km² (7,803 square miles), or 31.5 percent of the state’s surface area. It begins in Coahuila, flows through Nuevo León and into Tamaulipas, where it finally joins the Rio Grande near Camargo, Tamaulipas.

San Juan River in Worldwar
The Race established a town along the San Juan River, not far from the town of China, Nuevo León.

Penny Summers and Rance Auerbach followed the course of the river (which Auerbach thought of as a trickle) once they entered Nuevo León