Vast bar eaten away by gravel pits

TOOELE COUNTY — Stretching a mile and a half from South Mountain to the Oquirrh Mountains, flat-topped, a mile across with sloping sides, towering 200 feet above the valley floor, the Stockton Bar looks like a runway for ancient astronauts.

Instead, it's a dramatic sand- and gravel-bar formed by Lake Bonneville 15,000 years ago, a scientific treasure preserving records of waves and currents in the vast, largely vanished lake. Telling of days when mastodons roamed Utah, it records climate shifts from the last Ice Age.

And gravel pits are eating away at it. Their operations have chewed vast gray bites into the bar, which otherwise is earth-brown and gray with dry vegetation.

The pits are well within the law, dug on private land with rights affirmed by courts. Yet geologists are saddened by the relentless destruction of this feature, which is located beside state Route 36 between Tooele and Stockton.

Lake Bonneville covered much of the western side of Utah, reaching from above the Idaho border north of Logan, to the future sites of Ogden, Salt Lake City and Utah Lake. It overlapped the Nevada line, and part extended south of Milford. The Great Salt Lake, Utah Lake and Sevier Lake are remnants. The Little Sahara sand dunes of Juab County are part of its beach.

Formed by material dropping as currents shifted around mountains that formed islands in Lake Bonneville, the Stockton Bar is one of the lake's most impressive features.

It is the largest ancient lake-formed bar of its kind in America, said Marjorie A. Chan, a professor and the chairwoman of the Department of Geology and Geophysics at the University of Utah. "It's an important record," she said.

Detailed information is preserved in the layers and bumps of the Stockton Bar. Because it is scientifically important and yet easily accessible, "people actually fly in from all over the world" to examine it. "It's really kind of an icon."

Mark Milligan, a geologist with the Utah Geological Survey, recalled a meeting of the American Association of Petroleum Geologists in Salt Lake City. The group had visited Spanish Fork to examine a delta formation there, and dinner was next on the agenda.

"The people on our trip, much to my surprise, chose to drive from Spanish Fork to Tooele to look at the Stockton Bar, rather than eat dinner," he said.

Milligan said the "give and take" is that gravel operations slice open the bar, allowing scientists to examine internal stratigraphy. But then the section is gone.