Rocky Mountain Region

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 .

The Rocky Mountain Floristic Region, also known as the Rocky Mountain Floristic Province, is a floristic region within the Holarctic Kingdom in western North America (Canada and the United States) delineated by Armen Takhtajan and Robert F. Thorne. The region extends from Kodiak Island in Alaska to the San Francisco Bay Area and Sierra Nevada in California. The Vancouverian Province comprises the coastal part of the region for its entire length, including the Pacific Coast Ranges, and the Rocky Mountain Province includes the Rocky Mountains and associated ranges. There are no endemic plant families in the region but many endemic genera and species.