Since Sangaku-shinko faith originally developed from a form of animism faith worshipping nature, it took the form of syncretism of Shinto and Buddhism until the end of Edo period, but since this syncretism was banned under the order for the separation of Buddhism and Shintoism in the Meiji period, temples and shrines, including Dewa-sanzan Mountain, where Shugendo of the Shingon Esoteric Buddhism was strong, were separated, many of the main faith continued in shrines.
山岳信仰は、もともとが自然崇拝のアニミズム的信仰から発展してきただけに、江戸末期まで神仏習合の形態を取ってきたが、神仏習合が明治以後の神仏分離令により禁止されて以後、もともと真言密教系の修験道が強かった出羽三山も含め、寺と神社が分けられ、信仰の本体の多くは神社の形態を取って存続した。