The crew was preparing an area just west of 6th Avenue and Simms Street for retaining wall construction when they unearthed the fossils on Friday, said Kathy Berumen of the Denver Transit Construction Group.

The Denver Museum of Nature an Science sent representatives who identified the fossils as from the time just after the dinosaur extinction when mammals were just beginning to dominate the landscape.

"The fossil leavers were from ancient palm trees, ferns and flowering plants deposited on a river bank when buried with sand and mud," Berumen said.

Some fossilized tree stumps were also found.

"One of the truly incredible things about our area is that we can collect fossils that have a Denver street address," said Dr. Ian Miller, curator of paleontology at the Denver Museum of Nature and Science. According to Miller, these plants are the first forests to come back after the massive asteroid impact that occurred in Mexico that caused the extinction of the dinosaurs and devastated the world's ecosystem.

"Museum visitors find it amazing that discoveries like this happen right here under the footprint of the city. From a scientific perspective, this discovery adds to our knowledge about the evolution of life and the events that took place at the end of the time of the dinosaurs, their extinction and then radiation of the mammals following that extinction," Miller said. "This is a big find."

Miller and a crew of volunteers from the museum's Paleontology Certification Program uncovered approximately 1,400 fossils during the weekend of Friday, Sept. 11 and Saturday, Sept. 12.

The fossil leaves are now specimens at the Denver Museum of Nature and Science. They will be analyzed by scientists like Miller to determine the history and evolution of plants in the Denver basin.

The museum is currently looking for volunteers in the paleontology program. For more information, visit the Denver Museum of Nature and Science website.