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 or Paektusan (), 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 (), Mount Kumgang or Kumgangsan (), Mount Seorak or Seoraksan (), Mount Taebaek or Taebaeksan (), and Mount Jiri or Jirisan (). There are several lower, secondary mountain ranges 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.