Final answer:
John Muir, founder of the Sierra Club, influenced Theodore Roosevelt to conserve natural resources by setting aside forest reserves, establishing wildlife sanctuaries, and creating national parks.
Step-by-step explanation:
John Muir, the leading conservationist of the early twentieth century and founder of the Sierra Club, had a significant influence on President Theodore Roosevelt's environmental policies. Inspired by Muir's advocacy for nature and after their shared experiences in Yosemite National Park, Roosevelt was encouraged to take a stronger stance on conservation. He set aside 148 million acres of forest reserves, established more than 50 wildlife sanctuaries, and several national parks. While Roosevelt had a more utilitarian view on conservation, prioritizing the management of wilderness for the common good, he nonetheless recognized the importance of preserving America’s natural resources due to Muir's influence. This push by Muir towards greater environmental protection efforts is considered a pivotal moment in the American conservation movement.