While hundreds waited in line for tickets at the Wolf Trap box office, about 30 volunteers combed the park's woods along Wolftrap Run Branch and Wolftrap Creek from 9 a.m. to noon, picking up trash as part of the annual Potomac River Watershed Cleanup, sponsored by the Alice Ferguson Foundation. The park partnered with nearby Colvin Run Elementary School to bring students and their parents to the cleanup as a school community service project. Most of the local cleanups will be held this Saturday, April 8.