Here is a terrific post by Ann M. Little who blogs as Historiann: "Never Mind Slavery, Have You Dipped a Candle Yet?"
Little begins with a study that reveals that many plantation house museums in North Carolina "hardly mention slavery at all" even though slavery was their reason for existence. From there she riffs on other historic sites with similar amnesia (Indian missions without Indians for example). In some cases it turns out that the culprit is simply a lack of funding to update interpretations that were created generations earlier.
Which of our northwest sites suffer from similar historic amnesia?