I called all of the parks in the surrounding areas searching for camp sites for these unfortunate people. All motels were booked up too - and I had to send many of these people home. Many camp grounds are actually sold out for holiday weekends before you can reserve a site. There is a trick to this that many hard-core holiday campers use. Most reservation systems have a specific sale date.
Many parks sell camp sites up to six months in advance.
If you wanted camp sites for July 3rd and 4th you would not be able to reserve the sites until January 3rd. Here is the trick. If I decide to start camping from July 1st to July 4th I can make my reservations on January 1st, two days ahead of people who just want to camp on the holiday weekend. At the really popular parks, this is the only way to get a site on a holiday weekend. Please be aware that if you reserve a site, you are expected to occupy it.