A break in the rock record where layers representing different periods in time intersect - leaving gaps in time between to the two intersecting layers. For example, due to geologic upheaval, a 400 million year old layer of granite may have been desposited on top of a 600 million year old layer of sandstone. The respective layers represent a gap of 200 million years in geologic terms, yet they are intersecting. This phenomenon is called unconformity.

Unconformity in the Superstition Wilderness, Arizona

The Superstition Wilderness in Phoenix, Arizona is filled with geological unconformity.