In the south, the Shiwalik Hills are covered with dense Himalayan subtropical broadleaf forests, alluvial lowland river valleys, and mountains up to around  above sea level. The foothills descend into the subtropical Duars Plain, which is the eponymous gateway to strategic mountain passes (also known as dwars or dooars; literally, "doors" in Assamese, Bengali, Maithili, Bhojpuri, and Magahi languages.). Most of the Duars is in India, but a -wide strip extends into Bhutan. The Bhutan Duars is divided into two parts, the northern and southern Duars