You might be able to find what you are looking for in the San Juan Islands, or along the Washington or Oregon Coast. Do an internet search for Washington State Parks and a search for San Jaun Islands. Also try Dungeness Spit - near Sequim. I'm not sure how far you are willing to travel. I would not recommend traveling to the San Juan's on a holiday weekend. You will be waiting in ferry lines for hours - both going and coming. Deception Pass has a nice sandy beach at Cranberry Lake which is inside the Deception Pass State Park. Try Fort Ebey, Fort Casey, Fort Warden. Another thing you could do in a day is Jetty Island in Everett. A FREE short ferry ride to the man-made island. (Take a picnic lunch - and no dogs are allowed.) WEBSITE SAYS: Jetty Island is a two-mile long, man-made island with rare sandy beaches and shallow warm water located west of Everett at the mouth of the Snohomish River. The wildlife viewing and solitude for those who seek it have made Jetty Island a favorite for the entire Puget Sound area.
Jetty Island in Everett ...If this doesn't help, please give a little more detail of what you'd like - in particular, how far you are willing to travel.