Explore the new, interactive, digital map created from merging two United States Geological Survey (USGS) maps that depict the topography and geology of the United States. This composite is the most detailed and accurate portrait of the U.S. land surface and the ages of its underlying rock formations. The new map resembles traditional 3-D perspective drawings of landscapes with the addition of a fourth dimension, geologic time, which is shown in color.
This activity was designed to give students an opportunity to realize that all rocks weather mechanically and each specific rock type has its own particular rate of weathering. Students discover that mechanical weathering is the process of breaking down bedrock into smaller fragments by physical as opposed to chemical means and that rock weathering, although it seems to occur slowly in human terms, is an extremely significant part of the rock cycle.