Omonoimi Jinja (Oomonoimi / Ohmonoimi / Ohomonoimi Jinja) is a shrine in Yamagata that venerates Mt. Chokaisan. There are three shrine locations. The mountain itself is the Omonoimi-no-Kami. It is an active volcano and has erupted several times in recorded history.
Kita-no-yama, Awa-umi-dake, was the name of Chokaisan before it was renamed in the year 1342. This mountain marked the northern boundary of the land in olden days, and it protected against invasions. On the peak of Kita-no-yama is the honsha of Omonoimi Jinja.
Who is Omonoimi-no-Kami? In addition to the Kita-no-yama mountain, this kami is also Ooimi-no-Kami, Toyouke Daijin, and Kurakine-no-tama-no-mikoto (brother of Izanagi), according to shrine information.
The mountain became a place for the practice of shugendo. There are two gateway training centers in the foothills miles away from the peak. They are called the Warabioka-guchi and the Fukuura-guchi. They were both founded in about the year 564, more than 1400 years ago.
In the year 862, the shrines were listed in Engishiki as Myojin Taisha and Tsukiyama Jinja (Fukuura-guchi). Then it merged into a temple shrine, the Chokaisan Daigongen during the syncretic period. In Meiji times it separated and became the Omonoimi Jinja. It is the Dewa Ichinomiya.
Warabioka-guchi Site Visit
When we visited, I found it was a lovely place with stone lanterns, a large stone water basin, and a large hexagonal disc on the ground. There was no one there so we walked around and took pictures. In particular, I photographed the signboards. There were four hokura in the rear upper section of the keidai. It had been raining and it was pretty cold. Here are some photos numbered 0317-0360.
We were especially eager to see this shrine since it lists as one of the saishin the Toyoke-Ookami, fifth Takamimusubi of Hitakami and his other aspect, Ukanomitama no Mikoto.
Now that I have examined the posted map more closely, I wish I had climbed the kaidan to the top of the hill through the buna forest to see the ancient worship place.
Fukuura-guchi Site Visit
There was an office where I obtained a pamphlet from a guji-san. Although there is a map, it only shows the location of the honsha on the mountaintop and not the auxiliary shrines which are further down in the foothills.
This shrine is approached from one of the streets of the machi. Just inside the grounds there was an ike with a momiji tree in full color. The honden was up on the hill. It faced south. After looking around the upper keidai, we noticed on the right a path leading further up. We followed it and found nothing of interest. Still, it must lead to something. Regretfully there was no map to consult.
There is no doubt that the Warabioka site is ancient. The buna trees on the hill are remnants of a primeval forest. At the top of the hill are remains of an ancient place of worship. We know that the gateways served as training centers for the shugenja.
Although there is no hard evidence, it may well be that the Omonoimi Jinja are honoring Omononushi from the days of Hotsuma. He, as Ohonamuchi, provided for the people of the northern country as did the protector mountain Omonoimi Kita-no-yama. They are both Omonoimi-no-Kami!
Ohonamuchi, when he died, was named Utsushi-kuni-tama (removed spirit of the land) and became the deity Tsugaru Umoto (Great Original Deity of Tsugaru). Aya 10, JTC, http://www.hotsuma.gr.jp/aya/aya10-e.html