Ooka-yama is a trapezoid-shaped mountain that has been a symbol of the Tateyama region in the north-east of Yamagata City since ancient times. The summit of Ooka-yama commands views of Gassan and Murayama Ha-yama, as well as the northern parts of Yamagata City. There is also a shrine in dedication of Miyoshi Daimyojin.

All three trailheads to Ooka-yama are right near Tateyama Station on the JR Senzan Line, and many visit from all around. There are signs and the trails are well maintained making for a good hike. The mountain boasts many types of flowers such as Shojobakama (Heloniopsis orientalis), Katakuri Asian fawnlily (Erythronium japonicum), yamazakura mountain cherry blossoms, yamatsutuji (Rhododendron kaempferi), Himesayuri (Lilium rubellum), and Yamayuri golden-rayed lily or the goldband lily (Lilium auratum), among others. May in particular is a great time to take in the rhododendrons.

Kazama Fudo Trail (45 minutes one-way)

From Tateyama Station, head east (left) and while looking towards Ooka-yama, follow the Yamadera Kaido to the south. After turning to the east at the end of straight you’ll find the Minami Trailhead. After walking through the cedar forest you’ll come across the hall for the Kazama Fudo statue. Pass the statue and head up the zig zag trail through the forest until you reach the ridge. Head northeast (left), and once up the steep slopes, you’ll find the path to the summit.

There's enough space for two or three cars to park at the trailhead. Just to the north-east (lefthand side) of the Kazama Fudo statue hall there is a place to get spring water.

Nanamagari Trail (45 minutes one-way)

Head east over the Yamadera Kaido from Tateyama Station. At the end of the farm road, you’ll see the trailhead. There are steep slopes to navigate until you reach the ridge known as Nanamagari. Turn southwest (right) at Nanamagari, and after even more steep slopes, you’ll find yourself at the summit. Near the summit around where this trail meets the Kazama Fudo trail there is a stone statue of a Yamanba (see this article for more).

Kazama-san / Kyumatsutake-yama Trail (1 hour 10 minutes each way)

From Tateyama Station, cross the Yamadera Kaido and head through the residential area until you see the red torii gates that mark the trailhead. The trail lies past the hall with a giant bell and the Yakushi-do hall of Yamakami Jinja. After walking to the summit of Kyumatsutake-yama, head southwest (right), and go down until you meet the Nanamagari Trail. Follow the trail up 30 minutes or so until you reach the summit of Ooka-yama.