Paleontologists are finishing up their first dig in 30 years inside an unusual cave in northern Wyoming believed to hold the remains of tens of thousands of ancient animals.

The researchers aren't entirely sure yet what they found during their two weeks of digging at Natural Trap Cave, but they're planning further study back in their labs.

Bones that they discovered could include those of North American lions, short-faced bears and other now-extinct species from around 20,000 to 25,000 years ago, according to the Associated Press.

The only entrance to the cave is a 15-foot-wide hole in the ground that's almost impossible to see until you're right next to it.

Scientists say over the millennia, thousands of careless animals dropped 80 feet to their deaths within the chilly cave, according to AP.

A metal grate installed over the hole now stops people and animals from falling inside.

Scientists are hoping that the cave's humidity and cool temperatures might even preserve genetic material of extinct animals from the days when massive ice sheets last covered North America.

Bones found were packed in Rubbermaid containers for shipment to universities in the U.S. and overseas.

"It's an incredible site. It definitely is one of the most significant sites that BLM manages and it will provide very, very important information," said Brent Breithaupt, an American paleontologist as well a previous curator and director of University of Wyoming Geological Museum, according to the French Tribune.

This was Breithaupt's second visit to the cave.

During the previous excavations between 1974 and 1984 a tall stack of scaffolding helped researchers get in and out.

See Now: OnePlus 6: How Different Will It Be From OnePlus 5?