For those who love nature and would like to visit some national parks (Yosemite, Sequoia and Kings Canyon, Point Reyes, Channel Islands…), it is advised to buy the anual pass, for a $80 fee (available at any park entrance). This pass was released last January 2007 and gives you access to all national parks (400!) and federal parks (like Muir Woods) across the United States for a one year period. This pass is nominal (you write your name and the name of your partner) and gives free entrance for the entire car whatever the number of passengers.
Otherwise, each time you want to enter a park, you pay a fee per car valid for a couple of days (between $20 and $25 for national parks and less for federal parks). In other words, as soon as you visit 3 parks in a year, it is worthwile to subscribe to the anual pass.
Tip: In order to prepare your visits in the national parks, official web sites (National Park Service US departement) are gold mines. Go simply to your favorite search engine, type in the park’s name and check that the address starts with www.nps.gov/