The late was a time of active mountain building.

The Late Laramide orogeny was a time of active mountain building.

Explanation:

The Laramide orogeny can be described as a time of mountain building which took place during the Late Cretaceous period.

There is still a dispute over the beginning and ending time of the Larmide orogeny. Most of the rocky mountains which can be seen today can be attributed to this period. Deep-seated deformation was a major feature of the Laramide orogeny. During this period, mountain summits were close to sea level as compared to today.