Diggin' For Dinosaurs - Dry Mesa Quarry & Grand Valley

Vivian and Ed Jones had explored the high desert canyonlands west of Delta, Colorado, since the 1950s, looking for bones and arrowheads. As they hiked the hot, dry hills of junipers and pinyon pines one weekend in 1971, Vivian came across a rather large toe bone. She reported the find to Jim Jensen of Brigham Young University and brought him to the site. The following year, Jensen and others began excavating Dry Mesa, soon making several exciting discoveries and also generating a fair amount of controversy.

The first big discovery, in 1972, was an almost complete skeleton of Torvosaurus, a two-ton carnivore not previously encountered that may have rivaled Tyrannosaurus rex in size. (The toe bone found by Vivian Jones turned out to belong to Torvosaurus.) Later that year, Jensen found evidence of an even larger dinosaur, an eight-foot-long shoulder blade that belonged to what he dubbed Supersaurus. At the time it was the largest dinosaur known, believed to be more than 80 feet long and 50 feet high.

In 1979, Jensen found bones from what seemed to be an even larger dinosaur, which he named Ultrasauros. While Supersaurus has been accepted, other scientists disputed Jensen's claim for Ultrasauros, calling it simply a very large specimen of Brachiosaurus.

Nearly 10 years of digging later, in 1988, another monstrous bone emerged from the hillside: a 1,500-pound, six-foot-long pelvis that is probably the largest bone complex ever found and most likely belonged to Supersaurus. Palaeontologists continue to debate who has found the largest dinosaur in North America. Is it one of the Dry Mesa specimens, or are they overshadowed by Seismosaurus from New Mexico?

Several tons of Dry Mesa bones are still encased in plaster jackets and stored under the football stadium at Brigham Young University, waiting to be cleaned. No one can say how much bone remains in the ground at Dry Mesa, and whatever is left might be buried deep in the hillside. Uncovering more bone could require expensive and destructive heavy equipment. For the time being, though, the dig continues each summer, and visitors can watch the excavation from the side of the quarry.

Grand Valley, Colorado

Besides a pair of dinosaur museums, Colorado's Grand Valley offers a trio of trails that touch the past and present of palaeontology. Just north of I-70, at the Rabbit Valley exit 25 miles west of Grand Junction, the Rabbit Valley Research Natural Area includes the Mygatt-Moore Quarry, which, since its discovery in 1981, has produced about 2,000 bones from eight kinds of dinosaurs, including Mymoorapelta, North America's oldest armored ankylosaur.

The active fossil quarry marks the first stop on the shadeless 1.5-mile Trail through Time, where you can see a few real dinosaur bones left in place. Bring boots, water, and the informative trail brochure. Head a short distance uphill to the site where a partial Camarasaurus skeleton was found lying on its right side. The skull now resides safely in a museum, but eight articulated neck vertebrae are still partially exposed on a sandstone ledge.

Continued in: Diggin' For Dinosaurs - Grand Valley

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