Clayton Beach is closed to public access per the Washington State Parks website. It is unsafe to cross the train tracks to access the beach because they area active and trains do not have enough of a sight line for pedestrians in this area. See quote below.
"Previous access to the beach via unauthorized use of Burlington Northern Santa Fe property must be discontinued because of inadequate sight lines for pedestrians to see on-coming trains when crossing the rails to access the beach area. State Parks has plans for eventual construction of a rail overpass that will provide safe access to Clayton Beach, and Burlington Northern Santa Fe is in agreement with this plan."
However, in 2022, construction will begin on a hiking trail to allow for pedestrian access to this beach. Check back to see when this route is open to trail users.