Yosemite’s Hetch Hetchy Valley was dammed and flooded nearly 100 years ago, but the prospect of draining the reservoir continues to inspire romantic imaginings about unlocking a brand-new outdoor-recreation mecca in one of the country’s most popular national parks. If we could return Hetch Hetchy to a more natural state — of the variety that stirred John Muir’s soul a century ago — would we be clearing a path for the emergence of Yosemite Valley 2.0?