State laws govern what rights a landowner has regarding archeological remains on private property.
I do not know what the laws are in Washington state. However, for non- burial sites it is generally the case that the private property owner has control over an archeological site on his or her property. He or she may choose to protect the site, allow archeological examination of it, or destroy it. An exception to this occurs if the property is part of some sort of development project that requires a Federal permit or that is Federally funded. In this situation, the possible impact of the development project on archeological sites in the area must be examined through an archeological study.