Programs and Services

Geologic Mapping

Geologic mapping is central to the Idaho Geological Survey's research. Geologic maps are interpretations by scientists of the earth's surface and subsurface. Geologists use various analytical techniques to discover what lies out of sight and too deep to dig up. They know first of all that much can be revealed by an experienced scientist walking the ground and kicking rocks. To strengthen their judgment, they'll probably compare the chemical and structural composition of rocks from one place to another. They may also analyze samples of rock from drill cores or data from seismic profiles taken from deep in the subsurface. Their approach to defining the rocks may furthermore be influenced by what they are looking for. The same area of ground can be studied for different reasons. Beyond knowing an area's general geology, scientists create maps to locate minerals, geologic hazards, ground water and aquifers, waste sites, roadways, and urban development.

Urban Areas

The Survey is mapping the geology of urban areas in various parts of the state. Six 7.5-minute quadrangles have been completed on the Coeur d'Alene-Rathdrum corridor in northern Idaho. Three other quadrangles are currently being mapped in the same area of Kootenai County. Surficial geologic mapping has clarified geologic relationships in the Rathdrum-Spokane valley aquifer, the sole water source for the region. The findings are crucial to developing a hydrologic model of the aquifer system. Flood deposits in the area are also the prime source of construction materials. Sand and gravel, crushed rock, rip rap, and decorative boulders are important products in the region's rapid growth. Mapping will benefit both the aggregate producers and regional planners by identifying the locations and availability of these commodities.

For the Moscow-Lewiston region, four quadrangles have been published and three others are being mapped. This project is studying three geologic elements in the area: (1) the configuration of the Precambrian-Cretaceous basement; (2) the extent and stratigraphic relationships of the Columbia River basalts and associated sediments; and (3) the post-Miocene erosion and drainage development and the deposition and evolution of the Palouse landscape.

In the southeast, surficial mapping has been completed on the Pocatello South and Pocatello North quadrangles. The project extended the line of the giant gravel bar, the Michaud Gravel, deposited by the Bonneville Flood. Another prominent feature detailed in the mapping is the Pocatello Bench. This broad apron, north of the city and extending west from the Pocatello Range, is a relict coalescence of alluvial fans now buried by thick loess. The Bonneville Flood eroded the original, nearly flat surface, leaving the bench in its wake and depositing enormous loads of entrained gravel downstream as a gravel bar, now called the Michaud Gravel.

Digital Maps

The statewide digital geologic map database at the 30- x 60-minute scale is about 20 percent complete. The work is being done by the Survey's Digital Geologic Mapping Lab.