WHEN JOHN MUIR, the explorer and naturalist, hiked through the Hetch Hetchy Valley, he was captivated by the untouched wilderness that surrounded him. The remote valley lay some twenty miles north of Yosemite Valley in California's Sierra Nevada. The Tuolumne Indians who lived and hunted in the area called the fertile valley Hetch Hetchy, which means "a grass with edible seeds." By 1868, when Muir first trekked through the Sierra and made his home as a shepherd in the high country, only an occasional hiker or hunter who wandered along the isolated canyon knew of the stunning waterfalls and lush plant growth that made it so remarkable.

Muir saw the Tuolumne River as it tumbled over rocks through a deep gorge, lined with high rock walls colored yellow and red with lichens and shaded by live oaks and pine trees. "For miles the...