Andrew Carnegie contemplated the cavernous new wing of his Pittsburgh museum. It needed something to fill it. Something big.

There was that young fellow, Earl Douglass, in his employ with the story of a bone. What was it again? Oh, yes -- a thighbone bigger than a man. The man had been following up on stories of big bones found by sheepherders near Utah's Green River, and that's where he had seen it. Too heavy to carry out, he had left it. Carnegie sent the young man back to fetch it, along with the rest of the beast. That would be something to fill the empty museum space.

In the summer of 1909, Douglass was an accomplished field paleontologist when paleontology was barely a science. He had already discovered several dinosaurs and fossil mammals when he returned to Utah.

That dinosaurs had once been here was beyond question. Fossil bones had been weathering out of the rock for eons. In fact, the thigh he had left the season before had been flushed down from somewhere higher up in the sandstone cliffs. (Someone had made off with the bone in his absence, even though it had been earmarked.)

Douglass didn't care much about a single random bit of dinosaur, no matter how impressive. It would mean much more to find the bone in its original rock matrix. Then you had a chance of finding a whole dinosaur. A miner searches for the mother lode; Douglass was looking for the fossil bone bed.

Douglass knew that the area around Vernal had once been a river delta. Just as happens today, animals swept away by floods are deposited along sandbars. If the conditions are right, the bones become covered by silt and eventually turn into fossil rock. He scanned the broken hills near where the Green River today emerges through Split Mountain. He knew that a fossil bonanza lay just below the surface in these mountains.

Douglass had been up and down the ridges pecking away at the rock for most of the summer. On Aug. 17, 1909, he knew that time was running out. Unless something turned up soon, he would have to return to Pittsburgh empty-handed.

Scrambling up the layered ridge, Douglass would have known he was leaping millions of years in the matter of a few yards. His eye searched for the same gray sandstone strata that had yielded his -- now stolen -- diplodocus thighbone.

Suddenly, there it was. A line of huge vertebrae emerged from the rock.

Hiring local ranch hands to help, Douglass directed the excavation. The seven exposed vertebrae hinted at something big. However, the chances of these being part of a complete, articulated fossil skeleton, he knew, were slim. So as more of the beast was exposed -- pelvis, tail, limbs, neck -- Douglass' excitement grew and was scarcely lessened when only the skull was found to be missing. He had a near-complete apatosaurus.

Here was something fit for Carnegie's massive Hall of Vertebrate Paleontology!

More of the bone bed was exposed, revealing an unimagined wealth of Jurassic fossils. Thousands of bones and dozens of species were found. In 1915, partly to ward off souvenir hunters, the area was designated as Dinosaur National Monument by President Woodrow Wilson.

In 1957, the Quarry Visitor Center was built, dramatically encapsulating Douglass' bone quarry. An unstable foundation eventually led to cracked walls and fear that parts of the structure might come down on someone's head. Three years ago it was closed indefinitely.

Ironically, the Quarry Building was recently saved by a bad economy. A $13 million renovation will begin in spring of 2010 and could be finished in 2011, thanks to the stimulus package recently passed by Congress.

Pat Bagley is the coauthor of Dinosaurs of Utah. More about Earl Douglass can be found in Wallace Stegner's Mormon Country.