Often an archaeological or historical site requires research beyond the level of a survey in order to make a determination of significance of the resources and their eligibility for the National Register of Historic Places. For archaeological sites, this normally includes additional research on the findings at similar sites, combined with more intensive subsurface testing, including placement of selected larger excavation units. For historic resources, site assessment may require in-depth historic research, including oral history interviews, as well as additional photographic documentation. The end result of a site assessment is a determination as to whether or not the site is eligible for the National Register of Historic Places. Only eligible sites require further resource management.