WSGS releases geologic map of the state

(Cheyenne, Wyo.) – The Wyoming State Geological Survey has created an improved version of the Geologic Map of Wyoming, an important visual tool displaying a variety of geologic features, from different ages of rocks and faults to the state’s river basins and mountain ranges.

The 1:500,000-scale wall map includes a separate legend sheet and references. TheGeologic Map of Wyoming is available to purchase for $25 via the WSGS Online Store or as a free pdf download.

“The geologic map of the state is intended to better understand and evaluate our geologic features and history. It can also be used to evaluate groundwater, energy, infrastructure development, hazards, and environmental protection,” said Tom Drean, director of the WSGS. “The map is a good reference tool or to display on an office wall; the colors and features are outstanding,” he said.

This map represents a major project by the agency’s GIS staff, cartographers, and geologists. The goal was to develop a new and improved presentation of the original geology, which was hand-scribed and created in 1985 by authors David Love and Ann Christiansen of the U.S. Geological Survey. In 1994, cartographers digitized the geology.

Creating this new version involved superimposing various layers of data on the map, a standard practice for creating geologic maps. Esri’s ArcMap GIS (geographic information systems) mapping software was used to combine the various layers of data. Color patterns and letter symbols were used to represent the various geologic rock units. The base map layers depict background reference information such as landforms, roads, and boundaries. The background is a detailed and accurate graphic representation of natural features on the ground, specifically a representation of relief in the terrain.

“One of the challenges we had with updating the map was symbolizing the faults, which were numerous,” said Suzanne Luhr, GIS map editor of the WSGS. “We had to evaluate each one for proper placement and direction.”

WSGS cartographer Phyllis Ranz was responsible for overlaying and modifying the patterns from the original map. They cover more than 200 rock units, known as geologic strata. These designs are intended to help differentiate between the places or contacts where different rock units meet, such as where igneous rocks have intruded through sedimentary rocks, or where metamorphic rocks occur.

“One striking attribute in the new version of the map is the shaded relief background generated from a digital elevation model,” Ranz said. A relatively new technique (with Global Mapper software) was used to blend the digital geologic data with a shaded relief base to enhance both Wyoming’s geology and its varied topography. Prior to the use of sophisticated computer software, contour lines were used to show elevation on a topographic map and were scribed by hand. While the tools to create the maps have changed, the creative design work conducted by the agency’s cartographers continues. “This geologic map represents how we can combine science and art,” Ranz said.

Understanding and visually displaying where different rock types are located provides important clues about where groundwater, energy, and mineral resources exist, a major role of the WSGS, Drean said. “This map provides a template for future studies in a variety of disciplines, from geologic and tectonic research to hydrologic and environmental studies.

–Provided by WSGS