What force did John Muir think sculpted Yosemite Valley?

John Muir believed that glaciers were the primary force that sculpted Yosemite Valley. He argued that the immense power of glacial ice carved out the valley's distinctive U-shape, steep cliffs, and unique rock formations. Muir's observations and writings emphasized the role of glacial activity in shaping the landscape, which significantly contributed to the conservation movement and the establishment of national parks.