Variations in the color or growth of surface vegetation that indicate the outline of buried archaeological features, such as walls, pits, or buildings; visible by aerial observation or photography. These indications are revealed by the abnormal growth of overlying crops. Buried archaeological features such as walls stunt crop growth; ditches increase crop growth. Buried pits and ditches may retain moisture better than the surrounding subsoil and during a dry spell plant growth is often enhanced over such features.