Sites are distinguished by the presence of both artifacts and features. Common features include the remains of hearths houses. Ecofacts, biological materials (such as bones, scales, and even feces) that are the result of human activity but are not deiberately modified, are also common at some archaeological sites.
Archaeological sites form through processes that can be both natural and human-related. Cultural remnants which have been buried by sediments are in many environments more likely to be preserved than exposed cultural remnants. Natural actions resulting in sediment deposited include alluvial (water-related) or eolian (wind-related) natural processes. In jungless and other areas of lush plant growth vegetative sediment can result in layers of soil deposited over remains. Colluviation - the burial of a site by sediments moved by gravity - can also happen, although it is more rare. Human activities (both deliberate and incidental) also often bury sites. It was fairly common in many cultures for newer structures to be built atop the remains of older ones. The sediment in which a site is buried is termed the matrix.
Generally, evidence of human activity is not considered an archaeological site unless it exceeds fifty years (?) in age and yields more than a small number of artifacts or features.
Famous archaeological sites include: