Many of the US National Parks charge some sort of fee to get in, either a nominal day-use fee, or in the case of big, popular, and over-used parks like Yosemite, a hefty $20 per car entry fee.
Just as California's state parks are on the verge of closing (and our governor is talking about "selling state property" including San Quentin, which makes me wonder a bit about other state land), the National Park Service is instituting a series of fee-free days in our national parks.
Now's the time to get out and visit.
When I was young, I thought Yosemite was overrated, by the way. Then I saw it, and can't imagine not having it
For a listing of upcoming fee-free days, please check the NPS page about it
(Pictures below are of Lassen and Yosemite, two of my favorite parks.)