Its northern boundary line was fixed by the Guadalupe-Hidalgo treaty of 1848 and the Gadsden treaty of 1853; it follows the Rio Grande del Norte from its mouth north-westward to lat.
The Distrito del Norte is credited with a population of 7583 and has its capital at Ensenada (pop. 1026); the Distrito del Sur has a population of 40,041 and has its capital at La Paz.
Approximately one-half of the tobacco, 77,632 acres yielding 37,485 lb in 1902, is grown in the valley of the Cagayan river, and most of the remainder, which is of inferior quality, in the neighbouring provinces of Union, Ilocos Norte and Abra, and in Panay, Cebu, Masbate and Negros.
North of the Sao Francisco the watershed projecting from the plateau eastward toward Cape St Roque, known as the Serra da Borborema in Parahyba and Rio Grande do Norte where its direction becomes north-east, leaves a triangular section of the easterly slope in which the river courses are short and much broken by rapids.
Thus the Rio San Antonio suddenly disappears near San Antonio de los Banos; the cascades of the Jatibonico del Norte disappear and reappear in a surprising manner; the Moa cascade (near Guantanamo) drops 300 ft.
The largest of the rivers through which Argentina drains into the Plata system are the Pilcomayo, which rises in Bolivia and flows south-east along the Argentine frontier for about 400 m.; the Bermejo, which rises on the northern frontier and flows south-east into the Paraguay; and the Salado del Norte (called Rio del Juramento in its upper course), which rises on the high mountain slopes of western Salta and flows south-east into the Parana.
The Argentine part of the great La Plata plain extends from the Pilcomayo south to the Rio Negro, and from the lower terraces of the Andes eastward to the Uruguay and Atlantic. In the north the plain is known as the Gran Chaco, and includes the country between the Pilcomayo and Salado del Norte and an extensive depression immediately north of the latter river, believed to be the undisturbed bottom of the ancient Pampean sea.