The mountain range is a natural divider between the two major flat areas present in the prefecture: the Shōnai Region to the west and the Yamagata Basin to the east.

The main peak, Ōasahi Dake, rises to 1,870 m above sea level and is ranked among the 100 Famous Japanese Mountains.

The mountains feature deep canyons with alpine plants on their ridges and pristine Japanese beech forests on their lower slopes.

The source of the Sagae River, famous for its clear water, is located in the Yamagata Prefecture side.

Prior to its construction, the negotiation over the relocation issue between the government and residents derailed, and it took 19 years from the initial planning to the start of its operation.

The Gassan Reservoir covers 340 ha of area and has a large population of ayu, rainbow trout, salvelinus, and seema.

A deciduous forest mainly consisting of Japanese beech covers the mountains up to 1200 m above sea level.

The vegetation shifts to shrubs from 1200 m. The area, designated as wildlife refuge by the government in 1984, is inhabited by a wide variety of animals including Japanese dormouse, Japanese serow, Asian black bear, golden eagle, mountain hawk-eagle, goshawk, and peregrine falcon.

The mountain range has readily available trails on all four sides, but large snowpacks remain all year on many of its peaks, as they sometimes called the Tōhoku Alps.

During the Meiji period, the Iide Shrine located on the summit was worshipped by local residents.

The center can provide information on the landscapes, geography, geology, flora and fauna, and environment of the region.