It drains a large portion of the Middle Park basin in Grand County in the Rocky Mountains west of Boulder and southwest of Rocky Mountain National Park.

It rises at the continental divide on the north side of Berthoud Pass in the Arapaho National Forest.

It flows NNW past Winter Park, Fraser, and Tabernash, and joins the Colorado River from the south two miles west of Granby.

As it runs north for its first 8 miles, it is on National Forest land and is publicly accessible.

The only exception is as the river flows through private land in the town of Winter Park.