Mount Jii, Mountain summit in Toyama, Japan

Mount Jii is a 2,825-meter peak in the Hida Mountains, standing east of the Kumo-no-daira lava plateau in Toyama Prefecture. It is composed of andesite and dacite, and its summit is gently sloping, making it easy to lose the trail in bad weather. The neighboring peak to the west-northwest, across a valley, is Mount Baba.

Mount Jii is the high point of the Kurobe plateau, a lava plateau in the Hida Mountains of Toyama Prefecture, formed of andesite and dacite. The summit is gentle and easy to lose in bad weather. The nearby mountain huts are Kurobegawa Sanso, Suisho Goya and Mitsumata Sanso.

The name Jii-dake means "Grandfather Peak"; the neighbouring Ba-dake, "Grandmother Peak", lies across the valley to the west-northwest. The pair are named as a family, and the summit of Jii-dake is the gentle high point of the lava plateau of Kumo-no-taira.

Mount Jii is the summit of the Yunomatai lava plateau, reached by trails from the surrounding valleys; the nearest huts are Yunomatai Sanso, Suisho Goya and Mitsumata Sanso. The top is gentle and easy to lose the route on in bad weather, so carry a map and compass.

Mount Jii is the summit of the Yumonodaira lava plateau, a gently sloping peak of andesite and dacite where the trail is easy to lose in bad weather. Just west-northwest, across a valley, stands its companion peak Mount Baa (祖母岳), the "grandmother" to Jii's "grandfather".