This study involved a geological survey in the northern Yatsugatake area, central Japan, with the aim of identifying historic eruptive activity of the Yatsugatake volcano. White-colored thin deposits were noted in soil; because of their distribution pattern and particle components, these were determined to be volcanic ash deposits ("ash A" and "ash B"). Their AMS ages are the 14th and 9th centuries, respectively, with the deposit sources estimated to be located around Inagodake and north of the Mugikusa pass, respectively. It is assumed that a few magmatic eruptions of the Yatsugatake volcano occurred within the historical time period. The trigger of AD 887 sector collapse could not be identified in this study.