Geologic Mapping

Intro

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 geoscience. Our extensive 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 RockTalk: Mapping Colorado.

A geologic map depicts the aerial distribution of various rock types of different ages. Rocks are broken out into mappable units or formations. A formation is a rock type that is distinct enough to separate from the other rocks in the area, and thick enough to show accurately on the map. Each formation is represented by a unique symbol and color on the geologic map. The symbol indicates the rock’s age and formation name. The geologic pattern and symbol for each formation are usually overprinted on a topographic map.

GIS

Geographic Information System

(GIS) data are used to create many CGS products. Search the map section of our bookstore to see whether the product of interest is available as GIS shapefiles. You may also browse the general catalog for publications that include maps in pdf format.

We continue to expand our GIS Map Portal with new GIS dataset downloads and online maps.

CGS Disclaimer:

Colorado Geological Survey (CGS) is not responsible and shall not be liable to the user for damages of any kind arising out of the use of data or information provided by the CGS, including the installation of the data or information, its use, or the results obtained from its use. ANY DATA OR INFORMATION PROVIDED BY CGS IS PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Data or information provided by the CGS shall be used and relied upon only at the user’s sole risk, and the user agrees to indemnify and hold harmless the CGS, its officials, officers and employees from any liability arising out of the use of the data/information provided.

LiDAR

LiDAR (Light Detection and Ranging) is a remote sensing method that uses light in the form of a pulsed laser to measure the range (variable distance) between the sensor and the Earth (or whatever the laser is aimed at). The LiDAR sensor may be mounted on an airplane for localized mapping, and there are also dedicated satellite-based systems that can read elevations to the centimeter over wide areas of the Earth. The primary advantage of a LiDAR-generated topographic map is that the methods can ‘see’ through vegetation,

The CGS no longer serves LiDAR data because the State of Colorado has recently opened a new map portal—Colorado Hazard Mapping—that makes statewide LiDAR data directly available for download. Once you are at the Hazard Mapping site, look for the LiDAR Download tab at the lower center of the screen to get to a statewide map where you can select the area of interest and get the data directly as a ZIP package.

Other individual LiDAR map servers that are serving Colorado data include:

• USGS National Map has downloadable data from the 3DEP Program
• Colorado GeoData Cache has downloadable LiDAR data for Colorado
• OpenTopography.org map viewer of NSF-specific LiDAR data for Colorado
• OpenTopography.org map viewer of non-NSF LiDAR data for Colorado
• NRCS Geospatial Data Gateway

What is LiDAR?

LiDAR stands for light detection and ranging. This state-of-the art technology relies on the projection of millions of short laser pulses to the ground from a specially equipped aircraft. The result is extremely detailed ground elevation data. The data from these LiDAR reflections are collected by measuring the time it takes for the aircraft to receive each of the millions of laser reflections. The resulting data is then combined and converted into an elevation image that looks exactly like the terrain below the aircraft, including buildings, trees, roadways, creeks, and rock outcrops. Also, using powerful software the “raw” LiDAR data can be processed to generate a number of useful end products, including an accurate “bare-earth” terrain model where trees, vegetation, and man-made structures have been edited out.

How does LiDAR work?

LiDAR systems vary by manufacturer, but all use the following instrumentation: a laser source and detector; a scanning mechanism and controller; airborne GPS and IMU equipment; a high-accuracy, high-resolution clock for timing laser emissions, reflections, GPS/IMU, and scan-angle measurements; high performance computers; and high capacity data recorders. With these components, LiDAR data collection is possible:

1. A pulse of laser light is emitted and the precise time is recorded
2. The reflection of that pulse from the surface is detected and the precise time is recorded
3. Using the constant speed of light, the time difference between the emission and the reflection can be converted into a slant range distance (line-of-sight distance)
4. With the very accurate position and orientation of the sensor provided by the airborne GPS and inertial measurement unit (IMU) data, the XYZ coordinate of the reflective surface can be calculated.

How is LiDAR data used?

LiDAR offers many advantages over traditional photogrammetric methods for collecting elevation data. These include high vertical accuracy, fast data collection and processing, robust data sets with many possible products, and the ability to collect data in a wide range of conditions.

Because of LiDAR’s ability to penetrate vegetation, the data is used to map unknown young faults, more accurately locate previously mapped faults, and determine the potential for geothermal energy in these faulted areas. The data are also used for creating highly detailed maps of other geologic hazards, such as landslides, debris flows, rockfall, and areas prone to flooding. The maps generated are used by local governments for community planning as well as by emergency management agencies. Our geologic mapping program also relies on LiDAR data to precisely map the extent of bedrock units and surficial deposits that cannot be seen in vegetated areas.