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The National Park Service is offering free entry to Yellowstone and all national parks on Saturday, September 28, in conjunction with National Public Lands Day.

The nation’s largest single-day volunteer effort for public lands is now in its 20th year. Spokesman Al Nash says A seven-day pass to Yellowstone and Grand Teton National Parks is normally $25 for a private, non-commercial vehicle. Camping and other fees will not be waived. The NPS is waiving entrance fees on 11 days in 2013 as a way to encourage people to get outdoors and enjoy the remarkable landscapes and historical and cultural sites national parks have to offer. Entrance fees will also be waived on November 9-11, which is the Veteran’s Day holiday weekend.