The southern and western parts of the peninsula have well-developed plains, while the eastern and northern parts are mountainous. The highest mountain in Korea is Mount Paektu (2,744 m), through which runs the border with China. The southern extension of Mount Paektu is a highland called Gaema Heights. This highland was mainly raised during the Cenozoic orogeny and partly covered by volcanic matter. To the south of Gaema Gowon, successive high mountains are located along the eastern coast of the peninsula. This mountain range is named Baekdudaegan. Some significant mountains include Mount Sobaek or Sobaeksan (1,439 m), Mount Kumgang (1,638 m), Mount Seorak (1,708 m), Mount Taebaek (1,567 m), and Mount Jiri (1,915 m). There are several lower, secondary mountain series whose direction is almost perpendicular to that of Baekdudaegan. They are developed along the tectonic line of Mesozoic orogeny and their directions are basically northwest.