CASTLE ROCK, COLO. ? Scientists digging south of Denver say they have uncovered evidence of a lush and vibrant rainforest that emerged surprisingly soon after the asteroid collision that wiped out the dinosaurs 65 million years ago.

The fossils of more than 100 kinds of towering conifer trees, huge ferns and blooming flowers challenge scientists’ long-held assumption that a desolate Earth took about 10 million years to recover from the catastrophe and sprouted only a few dreary plant varieties for a long time.

Instead, the finding suggests that plant life at least at this now-dry prairie along Interstate 25 was flourishing as early as 1.4 million years after the impact. Some of the tree fossils measure 6 feet in diameter.

“It not only recovered, it went crazy,” said Kirk Johnson, paleontology curator at the Denver Museum of Nature and Science. He reported the findings in the latest issue of the journal Science.

In fact, scientists said it might be the earliest example on record of a true tropical rainforest.

Other plant fossil experts who did not participate in the study said the discovery was totally unexpected.

While one site cannot explain plant life around the world during that tumultuous period, experts said the Castle Rock fossils will compel them to reconsider the period of life immediately following the dinosaurs’ extinction, known as the lower Paleocene.

“I never would’ve put this so early in the Paleocene,” said Leo Hickey, paleobotany curator at Yale’s Peabody Museum. “A flora of this diversity and richness is really striking.”

In their study, Johnson and Denver museum associate Beth Ellis said a comparison of fossils before and after the apparent asteroid impact indicate that the forest is not a holdover from the days of the dinosaurs but something that sprang up later.

Also, Johnson said the plants that grew there are not the same type as those that grew during the pre-asteroid Cretaceous Period. Instead, they are more closely related to other plants that typically grew during the Paleocene.

The ancient rainforest was more vibrant than some tropical locations today. Museum researchers have identified at least 104 plant species at the Castle Rock site. In contrast, many modern research sites in Brazil contain 40 to 60 plant species, while a location in Peru contains as many as 293.

How a rainforest grew at the Castle Rock site remains unclear. Johnson believes it was nourished by humid Florida-like heat and 100 inches of rain a year, probably delivered by monsoons that brewed in an older, larger version of today’s Gulf of Mexico and an ancient sea covering what is now the northern Great Plains.

The site was discovered in 1994 by a state highway worker. It is scheduled to be demolished later this year in a road-widening project.