Perhaps the most disputed valley in all California, Hetch Hetchy (Hetch Hetchy Rd. past the Hetch Hetchy park entrance) was once a valley similar to Yosemite Valley [1], but is now a reservoir. Hetch Hetchy supplies famously clean, clear water (plus some hydroelectric power) to the city of San Francisco [2] and other parts of the Bay Area [2].
But many environmental activists see the reservoir’s existence as an affront, and lobby continuously to have O’Shaughnessy Dam torn down and the valley returned to its former state of natural beauty.
Links:
[1] http://www.moon.com/destinations/california/yosemite-and-the-eastern-sierra/yosemite-national-park/sights/yosemite-valley
[2] http://www.moon.com/destinations/california/san-francisco-and-the-bay-area