Of Gondwanan origins, the Chhota-Nagpur Plateau is composed of Precambrian rocks over 5.4 billion years old. It formed a bridge between the Satpura Hill Range that extends westwards across India and the Himalaya, allowing an exchange of species adapted to montane climates. Falling largely in Jharkhand and West Bengal, but extending into neighbouring states, this ecoregion has dry deciduous forests, with mainly sal Shorea robusta, besides Anogeissus, Terminalia, and Lagerstroemia trees, understorey shrubs, and grasses. The seasonal climate has cool winters, when nighttime temperatures may drop below freezing, and warm summers with temperatures reaching 35ºC. South-west monsoon rains (June – September) bring most of the annual average rainfall of about 1,400 mm.