The dig at the Ziegler Reservoir near Snowmass Village also uncovered two skulls of infant mastodons, about the size of a basketball, and the skull of a juvenile, about the size of a beer keg, The Denver Post reported Friday.
There are only three previous recorded mastodon finds in Colorado, and none included skulls, the newspaper said.
"Based on our previous research, we know that we are finding male and female mastodons of all ages," said Kirk Johnson, leader of the Denver Museum of Nature & Science's excavation team.
"Since beginning the dig last fall, we have uncovered 26 total mastodon tusks, which means we have evidence for at least 13 to 20 different mastodons on this site."
This is the Museum's second dig at the Ice Age site uncovered Oct. 14 when a bulldozer unearthed mammoth bones during work to expand the 15-acre reservoir to provide water for snowmaking at the Snowmass ski area.
In addition to mastodons, the remains of Ice Age mammoths, bison, deer and ground sloth have been discovered, the Post reported.