Construction workers preparing a site for new homes in Southern California have unearthed Ice Age fossils, including those of prehistoric bison, ancient mammoths, horses and turtles.

The project supervisor for the developer of the site, which is destined to feature hundreds of new homes, says the company has halted work to allow paleontologists to uncover and remove the fossils.

"I said, 'Take your time, this is kind of cool,'" said John Suster of Cornerstone Communities of San Diego.

The fossil find was made as workers began grading the site known as Quarry Creek in Carlsbad, north of San Diego.

Large construction projects in California involving the moving of large amounts of earth are required to have a paleontologist on site.

Still, Suster said he was surprised when fossil bones first started showing up.

"It's just rolling hills, nothing special," he said. "I don't think there's any way you could have known."

The fossils -- including the bison, only second ever discovered in San Diego County -- are from the Pleistocene Epoch, and are between 50,000 and 200,000 years old, says Tom Deméré, the San Diego Natural History Museum's curator of paleontology.

"It's really an exciting project in terms of the geology and paleontology," he said of the find. "The fossils have the potential to tell us a great deal about the climate, the environment, (and) the ecology of that time when they were living."

As each fossil is uncovered, work stops and the area is roped off to allow paleontologists to work, explains Cornerstone CEO Ure Kretowicz.

"They do a (plaster) cast in place, and then remove it," he says. "We stop everything or go grade another area on the site. Once they're gone, we start up again."

The paleontologists said the bison is by far the most exciting and unusual find.

A skull and partial skeleton was found, and although the exact species has yet to be identified, Deméré says it is probably an antique bison, Bison antiquus, or a giant bison, Bison latifrons.

"These are big animals, much larger than modern plains bison," he notes.

Fossil remains of at least two Columbian mammoths were also found at the Carlsbad site. The creatures stood 13 feet tall at the shoulder and at 8 to 10 tons larger and heavier than the better-known wooly mammoths of North American northern latitudes, the paleontologists said.