On certain days, national parks will waive entrance fees for everyone. It is also a day of service when thousands of volunteers participate in service projects across the country, including at national parks.
If you're looking to get out of the Bay Area, here's a full list of National Parks in California that also have free days:
https://www.nps.gov/state/ca/index.htm
* Be sure to click the "info" button to see if the park is open and also click the "fees" button to check if there's a fee.
Image Credit: Photo by Hari Manivannan on Unspash -
https://unsplash.com/photos/a-forest-filled-with-lots-of-tall-trees-_y2ADfRYdw4