In terms of hydrology, the Bravo, Purificacion, and Guayalejo Rivers flow into the Gulf of Mexico after crossing the state from the western inland. On their way, their basins and zones of influence naturally correspond to the areas destined for agricultural use. The Rio Grande, known to Mexicans as the Río Bravo, represents the northern frontier shared with the United States. One of the tributaries of this natural border, the San Juan River, feeds the Marte R. Gómez Dam. Agricultural and cattle-raising activities are served by 14 other dams across the state, with a total capacity of 7,500 million m3 of water.