Location: Northeast high jungle.
Area: 51,253 km2
Minimum: 190 masl (Pelejo)
Maximum: 3080 masl (Agua Blanca)
The territory of San Martín can be divided into four morphological zones: the western, near to the eastern side of the Andean Plateau, with a rough topography and many ravines; the zone of the wide valleys, with stepped terraces formed by the Huallaga River and its affluents, where population is engaged mainly in cattle and agriculture; the southwest zone, with a relief coming down from the Cordillera Azul, with low elevation, where is an impressive canyon known as Cajón de Sión, which finishes in the Cayumba rapids; and a little low jungle zone with areas easily flooded and with almost no accidents. The climate mainly warm humid, with a season without rains and nights relatively fresh.
The hydrographical axis of the department is made up by the mid course of the Huallaga River, which with its affluents, forms an hydrographical system which drain all of the department's territory. The "Pongo de Aguirre" is an important canyon formed by the Huallaga in going through the andean hills.
San Martín is considered the future "Peru's Granary" because of its proved possibilities regarding cattle and agriculture production.
Túpac Yupanqui entered and subdued the Inca dominion, the nowadays far away province of Moyobamba, known in that time with the native name, Muyupampa. In 1839, the spaniard Alonso de Alvarado reached the Mayo River and founded a city to which he named as Santiago de los Valles de Moyobamba, which later became the capital of Maynas. A great importance figure was also the Priest Manuel Sobreviela, who, between 1787 and 1790, accomplished travellings along the Huallaga River and, as a result, published a map named "Planning for the course of the Huallaga and Ucayali Rivers and for the Pampa del Sacramento".
On August 19, 1821, Moyobamba, capital of the department, was the first peruvian city in declaring its Independence. In the last years, the penetration highway has allowed for the increase of the exchange of different products, thus benefitting the economy of this department.