The Washington State Department of Natural Resources has a new “story map” series online that shows places to rockhound in Washington.
https://www.dnr.wa.gov/rockhounding
It also spells out the rules you should take into consideration for State, Federal and private land. Click on the Mineral and Fossil map option. The little spots on the map show collecting sites. You can zoom in to get a better idea of the locations but there are not always driving instructions or exact coordinates. What surprised me was that it shows many more collection sites for things like trilobites, fossils, petrified wood and gemstones than I knew about.