Nearly all of Nagaland is mountainous. In the north the Naga Hills rise abruptly from the Brahmaputra valley to about 600 meter and then increase in elevation toward the southeast to more than 1830 meters). The mountains merge with the Patkai Range, part of the Arakan system, along the Myanmar border, reaching a maximum height of 3826 meters at Mount Saramati. The region is deeply dissected by rivers: the Doyang and Dikhu in the north, the Barak in the southwest (India), and the tributaries of the Chindwin River in the southeast.
Nagaland has a monsoonal (wet-dry) climate. Annual rainfall averages between 1800 and 2500 mm and is concentrated in the months of the southwest monsoon (May to September). Average temperatures decrease with greater elevation; in the summer temperatures range from the low 21–23 °C to the high 38–40 °C, while in the winter they rarely drop below 4 °C, though frost is common at higher elevations. Humidity levels are generally high throughout the state.
Forests cover about one-sixth of Nagaland. Below 1220 meters are tropical and subtropical evergreen forests, containing palms, rattan, and bamboo, as well as valuable timber species (notably mahogany). Coniferous forests are found at higher elevations. Areas cleared for shifting cultivation have a secondary growth of high grass, reeds, and scrub jungle.
Elephants, tigers, leopards, bears, several kinds of monkeys, sambar deer, buffalo, wild oxen, and the occasional rhinoceros live in the lower hills. Porcupines, pangolins (scaly anteaters), wild dogs, foxes, civet cats, and mongooses also are found in the state. The long tail feathers of the great Indian hornbill are treasured for use in traditional ceremonial dress.