The availability of archaeological evidence for study is dependent on the natural conditions in which the archaeological remains are found; certain types of natural conditions favor preservation of organic substances and therefore lend themselves to sheltering well-preserved organic remains, while other types of natural conditions lead to the degradation or destruction of organic remains that may have existed. An important distinction in land archeology can be made between dryland and wetland archeological sites. The vast majority of sites are dry sites, which means that the moisture content of the material enveloping the archaeological evidence is low and preservation of the organic material as a result is quite poor. Wetland archeological sites are sites such as those found in lakes, swamps, marshes, and bogs; in these wetland archeological sites, organic materials are effectively sealed in an environment that is airless and wet and that therefore tends to foster preservation.
It has been estimated that on a wet archaeological site often 90 percent of the finds are organic. This is the case, however, only when the site has been more or less permanently waterlogged up to the time of excavation; if a wet site has dried out periodically, perhaps seasonally, decomposition of the organic material has most likely taken place. Organic material such as textiles, leather, basketry, wood, and plant remains of all kinds tends to be well preserved in permanently waterlogged sites, while little or none of this type of organic material would survive in dryland archaeological sites or in wetland sites that have from time to time dried out. For this reason, archaeologists have been focusing more on wet sites, which are proving to be rich sources of evidence about the lifestyles and activities of past human cultures.
A serious problem with archaeological finds in waterlogged environments is that the organic finds, and wood in particular, deteriorate rapidly when they are removed from the wet environment and begin to dry out. It is therefore important that organic finds be kept wet until they can be treated in a laboratory; the need for extraordinary measures to preserve organic finds taken from wetland environments in part explains the huge cost of wetland archaeology, which has been estimated to be quadruple the cost of dryland archaeology.
One wetland site that has produced extraordinary finds is the Ozette site, on the northwest coast of the United States in the state of Washington. Around 1750, a huge mudslide that resulted from the seasonal swelling of an underground stream completely covered sections of a whaling village located there. Memories of the village were kept alive by descendants of the surviving inhabitants of the village in their traditional stories, and an archaeological excavation of the site was organized. The mud was removed from the site, and a number of well-preserved cedarwood houses were uncovered, complete with carved panels painted with animal designs, hearths, and benches for sleeping. More than 50,000 artifacts in excellent condition were found, including woven material such as baskets and mats, equipment for weaving such as looms and spindles, hunting equipment such as bows and harpoons, fishing equipment such as hooks and rakes, equipment used for water transportation such as canoe paddles and bailers, containers such as wooden boxes and bowls, and decorative items such as a huge block of cedar carved in the shape of the dorsal fin of a whale and miniature carved figurines.
