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Lake Powell’s sagging waterline means a natural wonder that hasn’t been seen since the 1960s is emerging.

Gregory Natural Bridge, which once spanned the creek in southern Utah’s Fiftymile Canyon, completely disappeared under the waters of Lake Powell in 1969, according to the Natural Arch and Bridge Society.

Lake Powell was created in 1963 and its rising waters in subsequent years eventually meant the loss of the 127-foot long Gregory.

[Related: Lost Glen Canyon wonders reemerge as Lake Powell dries up]

Now, with Lake Powell and its larger downstream cousin, Lake Mead, expected to reach historic lows this year in the face of a 20-year drought, Gregory Natural Bridge will once again be visible.

Natural Arch and Bridge Society President Henry Wede said Gregory isn’t quite visible yet, but “it’s getting pretty close.”

Grant Willis, a geologist with the Utah Geological Survey, said Gregory formed “fairly recently” — somewhere in the ballpark of 1,000 to 20,000 years ago.

He said the top of the bridge’s sandstone is 50 feet below water when the lake is full.

But since Lake Powell’s waterline hasn’t been that high in decades, the top of Gregory Natural Bridge’s sandstone has been exposed for years, he said.

What hasn’t been visible is the eye of the bridge, the top of which is at an elevation of 3,552 feet.

How long it stays visible will be determined by the duration of the drought.

The Salt Lake Tribune previously reported that with snowpacks in the Colorado River’s headwaters at about 70% of normal and bone-dry soils, inflows into Lake Powell are expected to be 45% of normal this spring, according to the latest “24-month study” released by the U.S. Bureau of Reclamation. The lake is already 135 feet below full.

The Colorado supplies water to some 40 million people across the Southwest, including most Utahns, and irrigates 5 million acres. Now its declining flows are expected to result in shortages for the river’s Lower Basin states, which have historically tapped the river in excess of their allotted shares under a century-old interstate compact. Utah and other Upper Basin states, meanwhile, continue to push diversions that would further deplete flows.

What is a natural bridge?

Willis said people often use the term “land bridge” when referring to structures like Gregory, but “natural bridge” is a better term.

Natural bridges are formed when water runs through rock. Arches are also often formed by water, but are usually shaped by other sources of erosion like ocean waves rather than by stream or river flow, Wede said.

Willis clarified that natural bridges are a subset of arches.

Utah is home to somewhere between thousands and billions of arches, depending on how a person defines an arch, he said. For instance, a person could define an arch as anything they can put their arm through.

That’s why geologists refer to “significant arches,” which in simple terms refers to structures that humans perceive as natural arches.

For instance, “although a cavern might technically be a natural arch, it is more appropriately called a cavern,” according to information from the Natural Arch and Bridge Society. “Similarly, size determines whether a natural arch is significant. A peephole one inch in diameter might technically be a natural arch, but it is not a significant one.”

Utah contains more than half of the world’s significant arches, Willis said.

And while Gregory Natural Bridge isn’t one Utah’s top 10 or 20 significant arches, it’s still a “beautiful, significant feature.”

Lake Powell covers Gregory Natural Bridge

Information from the National Park Service History Electronic Library details how Gregory Natural Bridge was formally “discovered” in 1940 by Norman Nevills, but the site was well-known before then by surveyors, ranchers and travelers.

The transformation of Glen Canyon into Lake Powell began in 1963. Over the next several years, as Lake Powell filled up, Gregory Natural Bridge became a popular attraction to visit by boat. When boats could no longer squeeze through it, the bridge was a popular place to swim under.

Finally, in the spring of 1969, Gregory Natural Bridge disappeared completely underwater.

Gregory isn’t the only feature that was covered up by the creation of Lake Powell. Wede said rock art and Native American ruins also disappeared with Gregory, though it’s unclear if they still exist after decades underwater.

How to see Gregory Natural Bridge

Wede said as far as he knows, the only way to really reach Gregory Natural Bridge is by boat. The surrounding areas are full of canyons, “so unless you’re a rappelling rock-climber kind of person, they’re really just not accessible,” he said.

But for people who get out there to see it, Wede said the bridge might have a pinstriped look from the water leeching out the rock’s red iron content. Examples of this are visible all around Lake Powell, he said.

“It’s going to be an interesting photograph,” Wede said. “It’s not going to look like an Arches National Park arch.”

Willis added that if people make the trip to see Gregory Natural Bridge, rockfalls are always a risk. This is particularly true of Gregory, since so much of it has been underwater for so long.

“People just have to realize they’re taking an element of risk when they go into canyons,” he said. “Nobody on Earth can tell you that a rockfall is going to occur sometime in the future.”

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