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Paleontologists are excavating the first dinosaur ever discovered in Utah, 155 years after a geologist discovered the skeleton of the mammoth plant-eater during an Army engineering survey of the West.

When geologist J.S. Newberry found the bones of the Dystrophaeus on the confluence of the Colorado and Green rivers in 1859, he could dig out only a few and told others later that there were more to be removed. But the site's location was lost for decades, and the work hasn't continued until now.

The excavation started last week and included a special ceremony Thursday marking the discovery more than a century and a half earlier.

Soon after Newberry's discovery, the Civil War broke out and his report languished for about 17 years, said John Foster, the executive director of the Museum of Moab.

The report was buried when it was finally published, Foster said, and eventually the site's location above a canyon south of Moab was lost. Researchers rediscovered it in the late 1980s after a 12-year search.

Since then, Foster said it's taken years to come up with a plan and funding to pay for the excavation.

The project is now being paid for by a grant of about $9,000 from the nonprofit Canyonlands Natural History Association, Foster said.

The site is difficult to access, located on a steep sandstone slope about 250 feet above the canyon floor.

Equipment and large chunks of rock have to be ferried down the cliff face and walked out of the canyon, Foster said.

He said there's more bone than researchers expected, so the excavation work will continue into 2015 and possibly the year after that.

Once pulled from the sandstone, the bones of the long-necked, long-tailed vegetarian dinosaur are headed to the Natural History Museum of Utah in Salt Lake City to be studied.

Foster said it will take about a year to clean the bones from the surrounding rock and assemble what they have.

Some of the skeleton eventually will be displayed at that museum, while other parts will be lent to the Museum of Moab.

The bones are the oldest sauropod dinosaur bones in North America, so studying the skeleton will help paleontologists understand the origins of sauropods on the continent.

Foster said scientists also hope to discover if and how this particular specimen is related to younger sauropods, which scientists know relatively well.