In the central Canadian Rockies, the main ranges are composed of the Precambrian mudstones, while the front ranges are composed of the Paleozoic limestones and dolomites.

It was an early spring day in the central Rockies, chilly and intensely fresh.

The area of mild air, which will be chased by an approaching cold front, extended from the central Rockies to the Eastern seaboard and pushed temperatures 10 to 30 degrees above normal.

About half of that output comes from the three mines here in a sliver of stony verticality in the central Rockies called the North Fork Valley, about 40 miles southwest of Aspen.

The storm moved across the Intermountain West on the 27th and developed into a major winter storm across the northern and central Rockies and northern High Plains.

Around the United States, the only areas where temperatures were not above normal were parts of western Maine, the central Rockies and northern and western Alaska, according to the climate analysis center.

However, it was not initially recognized as a serious threat to coniferous forests in the western U.S. Aerial spraying apparently terminated some smaller epidemics in the southern and central Rockies; others subsided naturally.

Meanwhile, severe to extreme drought developed in the lower Midwest and Ohio Valley as well as the southern and central Rockies.

All of the mountains are a part of the Rockies and are at the transitional point between the central Rockies and the northern Rockies.

This faunal turnover coincides with the Laramide orogeny and the uplift of the central Rockies.