The hills of Sikkim comprise of gneiss’s and half-schistose rocks, making the soil brown clay which is usually poor and shallow. The soil is coarse with high content of iron oxide, which helps in the growth of evergreen and deciduous forests. Precambrian rocks also form a large portion of Sikkim and are much younger than the hills. The rock consists of phyllites and schists and is the reason behind the heavy landslides of Sikkim.

The climate varies from subtropical in the south to tundra in the north. The maximum temperature is 28 degree Celsius and the minimum is zero degree Celsius. One can enjoy the five seasons of winter, summer, spring, autumn and the monsoons here. Sikkim is one the few states in India with a regular snowfall. The snowline is around 6000 Mts.

Sikkim sits in the ecological hotspot of the Lower Himalayas. Owing to its altitudinal gradation, the state exhibits diversity within a small region with plants ranging from tropical to temperate alpine and tundra. Rhododendron is the state tree. Sikkim boasts around 5000 flowering plants, 515 rare orchids, 60 primulas species, 36 rhododendron species, 11 oak species, 23 bamboo varieties, 16 conifer species, 362 types of ferns, 8 tree ferns and 424 medicinal plants.

The fauna includes the snow leopard, the musk deer, Bhorals, The Himalayan Tahr, the Red Panda, The Himalayan Marmot, Gorals, The barking deer, languor, the Marbled Cat, Tibetan wolf, the hog badger, the jungle cat and the civet cat. Yaks are reared in the alpine regions mainly for their milk, meat and as a beast of burden. A total of 550 species birds are found in Sikkim, some of which are endangered.