Originally Posted by skidder

To expand on spinnaker's post, there are three different types of campsites: Those run be the federal government (such as national parks and national forests), those run by state governments (State parks), and privately run campgrounds (mostly recreational vehicle or 'caravan' sites). Federal sites can be booked on recreation.gov, not sure about each state but California is through the State Parks' website, and I have no clue about private campgrounds. Most are not a problem to get into without reservations in the 'off' seasons except for the most popular (such as Yosemite Natl Park in California), but try and reserve a few weeks in advance if you can.