We broke up our drive from Pullman to Vancouver, BC here, and had a lovely picnic lunch overlooking the river. Definitely recommend this by-donation museum, and bring some extra cash for their gift shop, as there are some great finds in there! Geocaching in the area makes the afternoon complete - plan a couple of hours to explore it all.
The best part about this place is the collection of petrified tree trunks that are outside among the goofy dinosaur recreations (like from some B-grade, 50's Japanese sci-fi flick). These trunks are very impressive.
We stayed in Ellensburg, and as we came from Boise on I-82 we had to go back on I-90 to visit. It was well worth it!
Amazing petroglyphs of millions year-old trees; well displayed and explained. So are the Indian rock paintings. The Center provides a beautiful viiew of the Columbia River. Then - as a bonus - a flock...