August 25, 1916, President Woodrow Wilson signed the "Act to Establish a National Park Service (Organic Act) 1916". At that time there were 35 National Parks and Monuments managed by the Department of Interior. Fifteen years earlier, President Theodore Roosevelt began his conservation efforts which ultimately protected approximately 230 million acres of public land. According to the National Park Service website:
After becoming president in 1901, Theodore Roosevelt used his authority to protect wildlife and public lands by creating the United States Forest Service (USFS) and establishing 150 national forests, 51 federal bird reserves, four national game preserves, five national parks, and 18 national monuments by enabling the 1906 American Antiquities Act.
Yellowstone National Park was created by Congress in 1872 and was the start of a global movement that has resulted in more than 1,200 national parks or the equivalent in more than 100 nations. In the U.S. it takes an Act of Congress to create a National Park. The 1906 Act for the Preservation of American Antiquities - also known as the Antiquities Act or the National Monuments Act - was signed by Roosevelt in June 8, 1906. The Act allows Presidents to create National Monuments.
President Obama used that authority to create San Juan Islands National Monument on March 23, 2013. It was the 133 National Monument. As of June 2016, Obama had created 22 National Monuments, George W. Bush created five during his two terms as president and also reaffirmed one of the 19 National Monuments created by Bill Clinton. Another one of Clinton's was redesignated a National Historical site by Bush. One of Obama's National Monuments was redesignated a National Historical Park by Congress.
Visit the NPS website for information about celebrations nation-wide.