The
Rocky Mountains begin in northern New Mexico, where the axial crystalline rocks rise to between the horizontal structures of the plains on the east and the plateaus on the west. The upturned stratified formations wrap around the mountain flanks of the range, with ridges and valleys formed on their eroded edges and drained southward by the
Pecos river to the
Rio Grande and the
Gulf of Mexico. The mountains rapidly grow wider and higher northward, taking on new complications of structure and including large basins between the axes of uplift. In northern
Colorado and Utah, the mountains become a complex of ranges with a breadth of . In Colorado alone, there are 54 summits over in altitude, though none rise any higher than Mount Elbert at . Turning more to the northwest through Wyoming, the ranges decrease in breadth and height. In
Montana, their breadth is not more than , and only seven summits exceed 11,000 feet (3350 m) with one reaching .