Loreto, an inland department of Peru, lying E. of the Andean Cordilleras and forming the N.E. part of the republic. Extensive territories, nominally parts of this department, are in dispute between Peru and the neighbouring republics of Brazil, Colombia and Ecuador (see Peru), and the northern and eastern boundaries of the territory are therefore not definitely determined. Loreto is bounded W. by the departments of Amazonas and San Martin (the latter a new department, with an area of 30,744 sq. m., taken from Loreto, lying between the central and eastern Cordilleras and extending from the 6th to the 9th parallels, approximately), and S. by Huánuco and Cuzco. The area of the department, including the territories claimed by Peru, is estimated at 257,798 sq. m. The population is estimated (1906) at 120,000. The aboriginal population is not numerous, as the thick, humid forests are inhabited only where lakes and streams make open spaces for sunlight and ventilation. With the exception of the eastern Andean slopes and a little-known range of low mountains on the Brazilian frontier, called the Andes Conomamas, the surface is that of a thickly wooded plain sloping gently towards the Marañon, or Upper Amazon, which crosses it from W. to E. There are open plains between the Ucayali and Huallaga, known as the Pampas del Sacramento, but otherwise there are no extensive breaks in the forest. The elevation of the plain near the base of the Andes is 526 ft. on the Ucayali, 558 on the Huallaga, and 453 at Barranca, on the Marañon, a few miles below the Pongo de Manseriche. The eastward slope of the plain is about 250 ft. in the 620 m. (direct) between this point and Tabatinga, on the Brazilian frontier; this not only shows the remarkably level character of the Amazon valley of which it forms a part, but also the sluggish character of its drainage. From the S. the principal rivers traversing Loreto are the Ucayali and Huallaga, the former entering from Cuzco across its southern boundary and skirting the eastern base of the Andes for about four degrees of latitude before it turns away to the N.E. to join the Marañon, and the latter breaking through the Eastern Cordillera between the 6th and 7th parallels and entering the Marañon 143 m. below Yurimaguas, where navigation begins. The lower Ucayali, which has a very tortuous course, is said to have 868 m. of navigable channel at high water and 620 m. at low water. North of the Marañon several large rivers pass through Peruvian territory between the Santiago and Napo (see Ecuador), nearly all having navigable channels. On the level plains are a number of lakes, some are formed by the annual floods and are temporary in character. Among the permanent lakes are the Gran Cocama, of the Pampas del Sacramento, the Caballococha—a widening of the Amazon itself about 60 m. N.W. of Tabatinga—and Rimachuma, on the north side of the Marañon, near the lower Pastaza.
The natural resources of this extensive region are incalculable, but their development has been well nigh impossible through lack of transport facilities. They include the characteristic woods of the Amazon valley, rubber, nuts, cinchona or Peruvian bark, medicinal products, fish, fruits and fibres. The cultivated products include cocoa, coffee, tobacco and fruits. Straw hats and hammocks are manufactured to some extent. The natural outlet of this region is the Amazon river, but this involves 2500 m. of river navigation from Iquitos before the ocean is reached. Communication with the Pacific coast cities and ports of Peru implies the crossing of three high, snow-covered ranges of the Andes by extremely difficult trails and passes. A rough mountain road has been constructed from Oroya to Puerto Bermudez, at the head of navigation on the Pachitea, and is maintained by the government pending the construction of a railway, but the distance is 210 m. and it takes nine days for a mule train to make the journey. At Puerto Bermudez a river steamer connects with Iquitos, making the distance of 930 m. in seven days. From Lima to Iquitos by this route, therefore, involves 17 days travel over a distance of 1268 m. The most feasible route from the department to the Pacific coast is that which connects Puerto Limon, on the Marañon, with the Pacific port of Payta, a distance of 410 m., it being possible to cross the Andes on this route at the low elevation of 6600 ft. The climate of Loreto is hot and humid, except on the higher slopes of the Andes. The year is divided into a wet and a dry season, the first from May to October, and the average annual rainfall is estimated at 70 in. though it varies widely between distant points. The capital and only town of importance in the department is Iquitos.
