San Martín is a region in northern Peru. Most of the region is located in the upper part of the Peruvian Amazon rainforest. Its capital is Moyobamba and the largest city in the region is Tarapoto.

The territory of San Martín can be divided into four morphological zones:

• the west, near 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;
• a small lower jungle zone with areas easily flooded and with almost no accidents.

The Huallaga River is one of the most important rivers in the region. It forms, together with its tributaries a hydrographical system which drains all of the region's territory. The Pongo de Aguirre is an important canyon formed by the Huallaga going through the Andean hills.