Mokoso Shrine, located in a grove of trees just south of Yakumo is an ancient shrine listed in the 8th Century Izumo Fudoki where it is called Momino Yashiro.
The three main kami are listed as Kunitokotachi, Kuninosazuchi, & Amenohohi. Kunitokotachi is one, if not the, primal kami that came into being after the separation of heaven and earth, I first encountered it/him at Ayo Shrine and more info can be had in that post. Kunitokotachi was an important kami in Yoshida Shinto, and also in Tenrikyo. Kuninosazuchi I had not encountered before. As with most kami there are a variety of different versions, but most agree that it is one of two patron kami of hills and passes that came out of a union between Oyamatsumi, a kami of mountains, and Nozuchi, another name of Kayanohime, a kami of grasses. Amenohohi was the first emissary sent from the High Plain of Heaven to negotiate the hand over of the land from Okuninushi to the Yamato, and is considered the ancestor of the Izumo Taisha priestly lineage.
There are numerous secondary shrines in the grounds, including Shiogami, Sagi, Inari, and most interesting of all, Toshitokujin, the kami of the New Year with roots in Onmyodo, the Japanese name for Yin-Yang divination. Toshitokujin has connections with Tondo matsuri,... link here
There was also an altar to Kojin, a rope serpent wrapped around the base of a tree. Like Omoto in my region, Kojin is immensely popular in eastern Izumo, yet is not well known elsewhere or in towns. The land kami represented by a straw serpent can be found the length and breadth of Japan....
The shrine had a small Zuijinmon that typically included a pair of old, wooden komainu. The small wooden komainu found inside gates and sometimes flanking the honden or in the main building are much older than the nowadays more common stone komainu found flanking the pathway into shrines which mostly seem to only date back to the Edo Period.