The National Park Service is offering free admission Tuesday to more than 100 national parks that usually charge entrance fees.
The fee-free day marks the first day of summer on June 21.
Other fee-free days remaining this year are Sept. 24, which is called Public Lands Day, and Nov. 11-13, Veterans Day weekend.
A complete list of national parks covered by the free entrance offer can be found here. The list includes many of the system's best-known parks, such as Grand Canyon in Arizona, Yosemite and Muir Woods in California, Rocky Mountain in Colorado, Everglades in Florida, Yellowstone and Grand Teton in Wyoming, Acadia in Maine, Cape Cod in Massachusetts, Arches, Bryce and Zion in Utah, and Shenandoah in Virginia.
Some park concessions offer deals on fee-free days. For the first day of summer, Swan Mountain Outfitters at Glacier National Park in Montana is offering $5 off standard trail rates for kids riding with a full-paying adult, $5 off per rider on groups of six or more, and $5 off for Montana residents. Details at http://www.parkpartners.org/Special-Offers-for-2011.htmler.