Cross Mountain Canyon

Location: Moffat County
Size: 2160 acres
Designated: 1997
Land Manager: Bureau of Land Management
 
Cross Mountain Canyon is a classic example of an "exhumed horst" cut by a superimposed stream.  This block of ancient sedimentary rock was folded, broken, and uplifted during the formation of the Uintah Mountains in the early Tertiary period.  These mountains were eventually worn down and buried in their own debris, then were again uncovered or exhumed by erosion as a new round of uplift began about 10 million years ago.  In the meantime, the Yampa river had established its modern course, and as the land rose, the river cut a deep canyon and exposed the structure of the mountain.  Vertical cliffs of Mississippian Madison Limestone rise to over 200 feet in height in the canyon, which is bounded on the west by a well-exposed fault zone.  Two rare plant species:  Penstemon yampaensis (Yampa beardtongue) and Cirsium ownbeyi (Ownbey thistle) and four endangered fish species occur in the canyon of the Yampa at this site.  Peregrine falcons may nest on the cliffs.