This is the Last Free Weekend for Washington State Parks
This is the last weekend you can visit the National Parks in Washington State for free! June 10th and 11th. June 10th is national "Get Outdoors Day" and so you do not need a Discovery Pass to visit any park this whole weekend. After this weekend a Discovery Pass is $30 for the year or just $10 a day according to the Discovery Pass website.
The next free pass day for the parks is on August 25th on the National Parks Service birthday celebration.