Who is known as the famous naturalist and conservationist associated with California's national parks?

John Muir is widely recognized as a key figure in the establishment and conservation of California's national parks. His advocacy for the preservation of wilderness led to the creation of several national parks, including Yosemite, which is one of the most famous parks in the state. Muir's writings and activism helped raise awareness about the importance of protecting natural landscapes and influenced the early conservation movement in the United States. His work laid the groundwork for the National Park Service, demonstrating his profound impact on environmentalism and conservation.

Other figures listed, such as Henry David Thoreau, are significant in the realm of environmental philosophy and literature but did not specifically focus their efforts on California's parks. John James Audubon is celebrated for his studies of birds and nature, contributing importantly to ornithology but not directly connected to the conservation of national parks in California. Ansel Adams is renowned for his stunning black-and-white photography of the American West, especially Yosemite, but he was primarily a photographer rather than a conservationist in the early advocacy sense represented by Muir. Thus, John Muir rightfully stands out as the most influential figure associated with California's national parks.