Rio Grande Del Norte, Or Rio Bravo Del Norte, commonly called simply the Rio Grande, a river of North America, rising in the S. W. part of Colorado, between the La Plata and San Juan mountain ranges. It flows E. for about 150 m., then bends abruptly S., entering New Mexico between the Sierra Madre and the main chain of the Rocky mountains, and flows through that territory to the Mexican border; thence it pursues a general S. E. course, separating Texas from Mexico, to the gulf of Mexico. Its entire length is estimated at 1,800 m. The upper part of its course is obstructed by rocky ledges and cataracts, and the lower part by sand banks and numerous wooded islands; but small steamers have ascended to Kingsbury's rapids, about 450 m. from the sea. The Rio Grande is subject to periodical floods, which commence in April, are at their greatest height in the beginning of May, and fall toward the end of June. For the greater part of the year it is fordable almost everywhere above the influence of the tide. The only important tributary is the Rio Pecos, which rises on the E. slope of the Rocky mountains, in N. E. New Mexico, flows S. through the E. part of the territory to the Texas border, and thence S. E. to the Rio Grande, which it enters about 500 m. above the gulf. Its entire length is estimated at 700 m.
At certain seasons its bed becomes dry. Both the Rio Grande and the Pecos flow for the most part through an arid region; but their valleys, which are generally from 1 to 4 m. wide, that of the Rio Grande expanding in places to 10 or 15 m., are productive when irrigated. The principal towns on the Rio Grande are Brownsville, Texas, about 35 m. from its mouth, and Matamoros, Mexico, opposite Brownsville.