The headwaters of the Yampa are in the
Park Range in
Routt County, Colorado as the confluence of the
Bear River and Phillips Creek, near the town of
Yampa. The Bear River, larger of the two, flows from a source of at Derby Peak in the
Flat Tops Wilderness. The Yampa River then flows north through a high mountain valley, through
Stagecoach Reservoir and Lake Catamount, before reaching
Steamboat Springs, where it turns sharply west. Below Steamboat Springs, the Yampa flows through a wider valley in the western foothills of the Rockies. It receives the
Elk River from the north, then passes the towns of
Milner and
Hayden.{{cite map After entering
Moffat County the Yampa passes
Craig and is joined by the
Williams Fork. West of Craig, the Yampa crosses arid, sparsely populated sagebrush country for about before reaching Cross Mountain Canyon, where the river slices a deep gap through the namesake mountain. Below Cross Mountain the Yampa enters the open valley of Lily Park, where it is joined by its largest tributary, the
Little Snake River. Further west it enters
Dinosaur National Monument, where it traverses more than of rugged canyons and rapids. The Yampa joins the Green in
Echo Park at
Steamboat Rock deep within the national monument, about from the Colorado–
Utah border. ==Watershed==