Mononobe Shrine, the Ichinomiya of Iwami, enshrines Umashimade no mikoto, the ancestor of the Mononobe. His grave lies on the hillside behind the shrine. The Mononobe are often portrayed as Shintoists who resisted the importation of the foreign "kami" of Buddhism, though how much of that was religious and how much was power politics is hard to discern, as the two are intimately linked.
The father of Umashimade was Nigihayahi who descended from heaven in a stone boat to what is now the Osaka area. In the ancient myths the distinction between heavenly kami and earthly kami is an important one. The heavenly kami represent the Yamato and their associated clans who invaded and took over Japan. The earthly kami are the ancestors of the rulers of the tribes of Japan that the Yamato supplanted. What is interesting about Nigihayahi is that he was not part of the group that descended with Ninigi to Kyushu.
So when Jimmu invaded Japan in what is known as his "Eastern Campaign", when he reached the area that is now Osaka he was defeated by a tribe led by Nagasune. Nagasune claimed that he followed Nigihayahi. Jimmu and Nigihayahi had a "you show me yours and I'll show you mine" session with symbolic weapons whereupon Nigihayahi realized that Jimmu was of the same lineage as he, that is to say, they both had the same origins, so he submitted to Jimmu and had Nagasune killed. Jimmu made Nigihayahi's son Umashimade the head of his guard.
So, if the Mononobe have their origins in "the high plain of heaven", the Korean Peninsula, and ruled over the area around present day Osaka, why is Umashimade buried in Iwami? According to the shrines founding legend, Umashimade was flying on a crane and landed here thinking it looked like a mountain in Yamato. The shrines crest if of a crane and crane statues are in the grounds. If we consider that the Mononobe were at the peak of their power in the 6th Century, the time Buddhism wa sintoduced to the Yamato court, and we consider that Izumo lost its independence and was incorprated into the confederacy led by Yamato around the 5th Century, then it would suggest that the Mononobe were placed here as a projection of military power to warn the Izumo to behave.