Aug. 26–Californians can enjoy the natural wonders of national parks such as Yosemite, Death Valley and Sequoia & Kings Canyon on the government dime this weekend as the parks system celebrates its centennial.

President Woodrow Wilson created the National Park Service on Aug. 25, 1916, and it will honor that date by waiving admission to all its 412 sites from Wednesday until Sunday. Those areas include national parks, monuments, battlefields, military parks, historical parks, historic sites, lakeshores, seashores, recreation areas, scenic rivers and trails. In California, that means urban parks such as Alcatraz Island and Golden Gate National Recreation Area, as well as rural favorites such as Joshua Tree and Lassen Volcanic national parks.

Visiting a park or historic monument doesn't require reservations in advance, but certain area may be overcrowded, making parking a challenge. Certain activities within parks require permits or tickets that must be handled in advance, such as hiking the Half Dome trail in Yosemite or taking the ferry to Alcatraz Island.

The park service is also celebrating with a massive social media campaign encouraging people to get out to the parks. In recent years they've put a particular focus on millenials and ethnically diverse visitors, especially Latinos. A recent study by the National Park Service found that only 11 percent of Yosemite visitors were Latino, despite the ethnic group making up 39 percent of the state's population.

The service is also using the occasion to advertise some of its least visited parks, which get far less foot traffic than tourist targets such as Yosemite. Two of the sites on the National Parks Conservation Association's least-visited list are in California: the Eugene O'Neill National Historic Site and the Port Chicago Naval Magazine National Monument, both in Contra Costa County.

Yosemite was the fourth-most visited park in the system in 2015, and the only park in California to make the top 10. It fell behind Great Smoky Mountains National Park in Tennessee, the Grand Canyon and Rocky Mountain National Park in Colorado.

Overall attendance to sites in the parks system reached an all-time high in 2015, at just over 300 million people.

Sammy Caiola: 916-321-1636, @SammyCaiola