Kolyma Highlands

(the Kolyma Range; Gydan or Gedan [a pass]), highlands located in the Northeastern Asiatic USSR, chiefly in Magadan Oblast of the RSFSR. The Kolyma Highlands consist of a system of ranges, plateaus, and ridges that divide the Kolyma Basin from the rivers of the Pacific Basin. They extend 1,300 km from the headwaters of the Ola and Buiunda rivers in the northeast to the sources of the Anadyr’ River.

Plateaus (short, ridgelike, granite massifs 1,500–1,800 m high) prevail in the southwest. To the northeast they give way to a series of ranges separated by tectonic basins, including the Maimandzhinskii Range (maximum elevation, 1,800 m), the Oloi Plateau, which is crossed by the Kolyma motor vehicle road, the Seimchan-Buiunda Basin, and the Omzukchan Range (maximum elevation, 1,962 m). The northeastern Kolyma Highlands are also made up of the Omsukchan Basin, the Korkodon Range, the Kedon Range, the Upper Kedon Basin, the Konginskii Range, and the Molongda Range. Between the Korkodon and Oloi rivers (in the Kolyma Basin) lies the plateau-like Omoloi Massif, which is composed of Proterozoic gneisses and crystalline schists.

The western part of the Kolyma Highlands is composed basically of Permian, Triassic, and Jurassic aleurolites and sandstones. In the east effusive deposits prevail. Gold, tin, and rare metallic ores are associated with the numerous Mesozoic granite intrusions. Deposits of hard and brown coal, as well as thermal springs, are found in the basins.

On the western slopes of the Kolyma Highlands the climate is sharply continental. The average July temperature is 8°-10°C, the average January temperature, — 40°C. The summer is dry. On the east are the wet windward slopes, where the average July temperature is 4°C, and the average January temperature, — 20°C. Approximately two-thirds of the Kolyma Highlands have no forests and are covered with mountain moss-and-lichen tundras and stone pines. The valleys and lower areas of the slopes of the ranges and ridges (up to 500 m in the north and 800 m in the south) are covered by open larch forests. There are floodplain forests on the floors of the valleys.