Earth Day and free National Park Week coincide

Earth Day is this Saturday. It's an event organizers call the "birth of the modern environmental movement". 

This year, Earth Day falls during National Park Week and visitors will be able to get into all national parks, such as Yosemite, for free this Saturday and Sunday. 

National Parks officials are inviting Americans to join a volunteer project or simply to enjoy the natural wonders and wildlife preserved in national parks. 

An Earth Day rally is planned for San Francisco's Civic Center on Saturday, April 22nd from 10 a.m. to 6 p.m.