One motorist was killed and another seriously injured in a motorcycle crash on Colorado Highway 24 near Calhan early Tuesday, according to the Colorado State Patrol.

Investigators said an eastbound 2015 Harley Davidson, occupied by a man and a woman, slid off the right shoulder and down a steep embankment. Both riders were thrown from the bike as it flipped, officials said. Neither rider was wearing a helmet, authorities reported.

Both riders were taken by helicopter to a nearby hospital. The woman, 33, died at the hospital; the man, 36, is listed in serious condition. Officials did not identify either rider.

The crash, which was reported at about 5:50 a.m., took place several hours before it was called in, according to the State Patrol.