Final answer:
The statement is true; John Muir's conservation work and advocacy greatly influenced the establishment of Yosemite National Park in 1890.
Step-by-step explanation:
The statement about John Muir and his role in the establishment of Yosemite National Park is true. Muir, who was a leading conservationist in the early twentieth century, founded the Sierra Club and was instrumental in the movement to preserve the California's Sierra Nevada Mountains, which included Yosemite. His advocacy for the protection of these lands, along with other important figures and the federal government's evolving perspective on land preservation, ultimately led to Congress establishing Yosemite National Park in 1890.
Indeed, the protection of Yosemite had started earlier when, in 1864, President Lincoln signed the Yosemite Grant Act, securing protection for the Yosemite Valley. However, the creation of the national park itself is attributed to later efforts by conservationists, including John Muir, and actions by Congress. John Muir's work, including his collaboration with President Theodore Roosevelt, significantly influenced public opinion and government policies towards conservation and the establishment of national parks.