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The U.S. National Park Service will celebrate its 100th birthday on August 25th. To celebrate, there are many events scheduled during the month of August at parks all across the country. This upcoming weekend (Thursday, August 25 to Sunday, August 28th), admission for visiting over 400 parks will be waived. The Washington State park system is also waiving fees this weekend so be sure to check with the parks in your area.
If you are unable to make it to a national park this weekend, there are still two more chances this year for free admission. Check out this link to find out more information.
Link: http://www.nationalparks.org/connect/blog/2016-free-admission-days-national-parks
If you are 62 or older, please take advantage of this. Senior lifetime passes are going up from $10 to $80 on August 28. Get your pass by August 27. You are better off going to the park in person, but you can also do it online, for a fee of $10. You need some form of identification with your birth date and picture. I used a driver's license.
You can find more information here: https://store.usgs.gov/pass/PassIssuanceList.pdf
This is a page about camping at national parks. Some of the most beautiful places for camping, in our country, are protected as part of the National Park system.