Scientists released a report Tuesday about an unearthed graveyard of fossilized whale skeletons found alongside a Chilean highway.

The whales were discovered more than 120 feet above sea level in ancient sandstones below what is now the Pan-American Highway in the Atacama region in northern Chile, according to the Washington Post. Highway construction workers first found the fossilized whales, and called a nearby museum.

Scientists went to investigate, and found what turned out to be one of the most extraordinary marine mammal fossil sites in history.

Scientists discovered more than 40 skeletons of baleen whales in four different areas, suggesting four mass standings over a period of more than 10,000 years.

The site also includes two seals, an extinct species of sperm whale, an aquatic sloth and a walrus-esque toothed whale. Most animals were fossilized belly-up, meaning they died at sea or shortly after washing ashore.

Nick Pyenson, the curator of fossil marine mammals at the Smithsonian's National Museum of Natural History, said that the likely cause of the mass strandings were deadly algal blooms, also known as red tide. He added that it is the only thing that could have killed animals high on the food chain.

Pyenson is the lead author of the paper describing the fossils, which was published Tuesday in the journal Proceedings of the Royal Society B.

Scientists are estimating the age of the rock formation, and the skeletons, between 6 to 9 million years old.

The tidal cove where the whales and other mammals washed ashore has been lifted above sea level by the tectonic forces that also created the Andes Mountains.

Whale bones have been known to exist in the site for years, which is why the site is called Cerro Ballena, or "Whale Hill." But construction workers found the extraordinary cache of fossils when working on highway expansion in 2010.

The bones show no sign of being scavenged before they were buried and fossilized.

"I was blown away the first time I saw it. I didn't appreciate the scale of what was described to me," said Pyenson.

A new paper on the fossils features 14 co-authors from the U.S., Chile and Brazil.

Richard Norris, a paleontologist at Scripps Institution of Oceanography, said whales are usually found singularly, so the find is extraordinary.

"Whale fossils are not common. Having articulated whale fossils is even less common," he said. He also said that a trove of fossils that includes animals of different ages "is vanishingly rare."

The bones had to moved to be excavated, which was not an easy process.

"I don't wish a whale skeleton on anyone - it's a logistical nightmare," Pyenson said. "It's a big problem just to excavate one, let alone that number."

Pyenson recruited a team of technicians called the "laser cowboys" to create a 3-D digital record of the skeleton arrangement. The bones were then excavated and shipped to museums.

Pyenson believes the Cerro Ballena site is as extraordinary a discovery as the La Brea Tar Pits, from which mammoths and other extinct mammals were found and excavated. He said that hundreds of other fossils could still be hidden in the Cerro Ballena site.