I got news from US National Parks website. They have a special fee free program at more 100 national parks.
Mark your calendars for fee-free weekends this summer:
June 20-21, 2009 (Father’s Day weekend)
July 18-19, 2009
August 15-16, 2009
And to make the fun even more affordable, many national park concessioners are joining the National Park Service in welcoming visitors on this summer’s fee free weekends with the their own special offers.