If visitors to Washington state parks don't want to shell out $30 for the annual Discover parking pass, they can earn one by volunteering 24 hours of work cleaning up beaches, building trails or planting trees.

Volunteer service is a little-known option for acquiring the permit that the state started requiring in 2011 to help maintain parks.

Parks also are open a few days each year for people without passes.

But parks officials really hope more people buy the passes. They need the money to operate 100 state parks and other recreation areas.