EDIT February 22, 2010: Pictures removed after communication from Lee Rentz (see comments).
Dale Croes has been doing great work for years on wet site archaeology, most notably a long association with the Hoko River wet and dry sites on the Olympic Peninsula. More recently he has spent a decade or so at the Squaxin Tribe’s Qwu?gwes waterlogged site near Olympia, Washington. I see that Lee Rentz’s Photography blog has a nice photo essay on the Qwu?gwes site called Ghosts Dwell in the Lowering Tide.
Wet sites can produce locally anaerobic (oxygen depleted) environments, preventing or slowing bacterial degradation of organics. This allows survival of many artifact types which rapidly deteriorate in normal archaeological settings. At Hoko, there are well preserved wooden artifacts over 2,000 years old, at Qwu?gwes the material is mostly about 700 years old. Similar sites elsewhere on the Northwest Coast are mostly less than 5,000 years old, with the notable outlier of Kilgii Gwaay, which is 10,500 years old. Since some estimates put wood artifacts at 90% or more of NW Coast technology, you can imagine how revealing these rare, and increasingly threatened, waterlogged sites are.
The photos at Lee Rentz’s blog are excellent, and the text is accurate and informative. Good to see! If you want to find out more, some scholarly and other articles can be downloaded here, or you can work at Qwu?gwes yourself as part of a field school.