YOSEMITE NATIONAL PARK – As summer rolls up so do the cars and RVs to the gates of this storied natural church, with its luxurious meadows and towering granite walls. But about 25 miles before reaching Yosemite, my friends and I hung a left and disappeared down a road less traveled.

The Hetch Hetchy entrance to the park is a gateway to Yosemite Valley’s breathtaking cousin, a once parallel world of canyons and valleys now lined with hikes that trace the outline of a still-controversial reservoir that feeds San Francisco 167 miles to the west.

As four friends making an annual trek to a new corner of the Golden State, our mission was simply to take in new vistas and get some exercise. What we didn’t realize was how much our 14-mile hike around Hetch Hetchy would make us look not around, but down.

Peering into the dark blue waters of the reservoir, one question echoed: What did it look like beforethe Tuolumne River rose hundreds of feet? By most accounts the answer is: stunning.

Whether it’s a still-life by fabled Western painter Albert Bierstadt that depicts a tranquil Native American paradise teeming with wildlife and flora, or the passionate preservationist appeals of environmentalist John Muir, whose Sierra Club led a 12-year battle against the reservoir, all evidence points to the submersion of a slice of heaven to quench the thirst of Bay Area residents burned by the waterless inferno of the 1906 earthquake.

READ MORE: Yosemite National Park Guide

The two sides squared off one hundred years ago, with Muir arguing that flooding the Hetch Hetchy Valley was akin to damming “the people’s cathedrals and churches, for no holier temple has ever been constructed by the heart of man.” Proponents argued that the valley’s flat-bottomed, steep-walled shape made it perfect for a reservoir, and that the public still had nearby Yosemite to commune with nature.

Ultimately, pro-reservoir forces won, and in 1913 Congress passed the Raker Act, which granted San Francisco officials the right to block up the river. Work on the O’Shaughnessy Dam started in 1914, and 20 years later crystalline high-country water began flowing into San Francisco kitchens and bathrooms, much as it does today.

Not that the controversy has abated. The Sierra Club continues to fight for the restoration of the valley, while many local politicians oppose the idea (San Francisco Mayor Ed Lee called the notion of taking down the dam “stupid”). In 2012, San Franciscans rejected a ballot measure that would have funded an $8 million study on how the Hetch Hetchy Valley could be returned to its native state.

Wherever one rests on the issue, standing on the O’Shaughnessy Dam and looking east across the endless expanse of water corralled in by this spectacular cleft in the Sierra Nevada range is to behold beauty. Our hike snaked along the north rim of the reservoir, past two thundering waterfalls whose frigid spray was a welcome relief from the unusual 104-degree heat.

About four miles in, the trail cut north toward Rancheria Falls, a midday picnic spot like few others. Water rushing down from alpine peaks raced across an expanse of rocks, some of it pooling into natural tubs. We held our breaths and dipped in.

We spotted a few fellow hikers; some were heading deeper into the backcountry, others were only out for the day like us. A British couple couldn’t stop marveling at the sights and the lack of crowds, the husband noting that he’d “been to Yosemite countless times, but this is only my first time to Hetch Hetchy and now I’m kicking myself.”

In fact, we spent more time on the lookout for bears and rattlesnakes than other humans. Being alone in nature is tough these days, especially in a popular national park. For that reason alone, Hetch Hetchy is gift. Although one can be certain that Muir’s response to that assessment would be a shrug. Beautiful, yes, he’d say, but you couldn’t see what you missed.