Geologic Mapping

Geologic mapping involves plotting the location and attitude of the various rock units, faults, and folds on a base map. Geologic maps are used to investigate geologic hazards, mineral resources, groundwater aquifers, and just plain science. Our detailed geologic mapping program is conducted under the STATEMAP part of the National Cooperative Geologic Mapping Program (NCGMP). To learn more about geologic mapping, view our Geologic Mapping RockTalk.

A variety of questions arise when people learn that we are doing geologic mapping, such as:

  1. Hasn’t the whole state already been mapped? You sell the Geologic Map of Colorado.
  2. Geologists have been mapping in Colorado for 150 years. Why are you still mapping?
  3. What could you possibly learn after 150 years of study by some of the world’s best geologists?
  4. Isn’t the USGS doing mapping in Colorado?

Answers for those questions:

  1. The Geologic Map of Colorado is a wonderful map, but it is at a scale of 1:500,000, or about 8 miles to the inch — not very useful for detailed work. The fundamental scale for useful geologic maps is 1:24,000, or less than 1/2 mile to the inch. This scale of detail is called seven-and-a-half-minute-quadrangle mapping. Of the nearly 1,800 quadrangles in our state, only 418 are mapped at this scale. CGS currently maps an average of seven new quadrangles per year.
  2. Much of the earlier mapping focused on the bedrock geology in mining districts and did not pay much attention to the Quaternary geology (landslides, debris fans, glacial deposits, etc.) that is so important to good land use planning and understanding geologic hazards. Further, we have learned a lot in 150 years, so that our geologists can call upon that knowledge as they conduct today’s mapping. Much of the earlier mapping focused on the mountains. Most of our mapping focuses on areas of high growth potential, in order to have sound science for policy makers to base their land-use decisions.
  3. Amazingly, every summer our mappers uncover wonderful new discoveries that were not previously known. Colorado has incredibly diverse and complicated geology. With a state this complex, there are still a tremendous number of mysteries to unravel. In mapping geologic hazards across the state, the information from one area helps to understand another area.
  4. Historically, the federal geological survey conducted most of the detailed geological mapping in the U.S. However, in the past two decades, the state geological surveys have assumed this responsibility under the STATEMAP program.

Geologic map of the Morrison quadrangle near Denver, draped over a digital elevation model with a geologic cross section below.

Our Facebook page Colorado Geological Survey