(upper course called Levyi Oloi), a river in Magadan Oblast, RSFSR, a right tributary of the Omolon River of the Kolyma River Basin. It measures 471 km long and drains an area of 23,100 sq km. Originating in the Kolyma Highlands, it flows northwest along the southern slope of the Oloi Range; the lower Oloi flows in a wide valley. The river is fed by snow and rain. It freezes in October, with extensive aufeis (thick ice sheets that form on a river’s floodplain) in the upper course and large open water spaces in the midst of the ice along the entire course. The ice breaks up in late May.

a mountain range in Chukchi National Okrug, Magadan Oblast, RSFSR. It forms the watershed of the Oloi River in the south and the Oloichan and Pezhenka rivers in the north. Length, 350 km; elevations, to 1,797 m. The mountain range is composed of sandstones, aleurolites, and andesite tuffs. The tuffs have intrusions of granodiorites. The slopes are covered with dwarf stone pine and mountain tundra vegetation; there are dwarf larch forests in the valleys.