For example, the sharpening of a single stone tool in a camp by knocking off some flakes may be disturbed by other members of the camp. Most data consists of broader patterns resulting from many similar events at the same location. Many women may have gone out and foraged for plant foods every day for several weeks, and returned with them to the camp. The accumulation of plant food remains forms a broad pattern of economic choices that illustrate to the archaeologist which foods were important at this camp during the season of occupation. This is why sheltered sites in caves or under overhangs are so important.
Preservation tends to be excellent.
The Indians made most of their cutting edges from hard materials. Stone that has a conchoidal fracture, like glass, was the preferred tool material. Obsidian is volcanic glass. Glassy basalts were also used. The majority of the artifacts made in the Pacific Northwest were made from wood and fiber.