In 1970, hottate bashira (earthfast post) remains of a building dating from the first part of the Heian period were discovered at the site of Yokoe Manor and the area was nationally designated a historic site in 1972.
昭和45年(1970年)、同荘園跡から平安時代初期の掘立柱建物跡が検出され、同47年（1972年）に国の史跡に指定された。