Shimoshiraiwa is an important place for learning about the formation of the Izu peninsula. The geological stratum of the region is approximately 11 million years old and includes many fossils of shellfish, coral, and other organisms. Among these, Lepidocyclina, a type of Foraminifera, was found here. Lepidocyclina lived in shallow seas in the tropics and subtropics, thus its fossils provide an important proof showing Izu was once in a more southern location.