Updated

This fall San Franciscans will vote on a local measure that could return to the American people a flooded gorge described as the twin of Yosemite Valley.

Voters will decide whether they want a plan for draining the 117-billion-gallon Hetch Hetchy reservoir in Yosemite National Park, exposing for the first time in 80 years a glacially carved, granite-ringed valley of towering waterfalls.

The city leases the valley for $30,000 a year.

The measure could eventually undo a controversial century-old decision by Congress that created the only reservoir in a national park. It pits Republicans and environmentalists against Democratic San Franciscans, led by Sen. Dianne Feinstein, who are fighting for the city's pure water supply.

If the measure passes, voters would decide in four years whether to carry out the plan.