But why not purchase an Annual Discover Pass (just $30 plus fees) so you can visit your favorite state park any time you wish! http://wdfw.wa.gov/licensing/discoverpass/
2015 Free Days
Jan 18-19: Martin Luther King, Jr. Day
Mar 19: State Parks' 102nd birthday
Apr 4: Saturday Spring Day
Apr 22: Earth Day
May 10: Sunday Spring Day
Jun 6: National Trails Day
Jun 13: National Get Outdoors Day
Aug 25: National Park Service Birthday
Sept 26: National Public Lands Day
Nov 11: Veterans Day
Please note, free days apply only to day use (not overnight stays or rented facilities). A Discover Pass is still required to access lands managed by the Washington State Departments of Natural Resources and Fish & Wildlife on these days. Sno-Park permits are still required on free days at designated Sno-Parks during the winter season.