BEDROCK GEOLOGIC MAP OF THE RALEIGH, NC 1:100,000-SCALE QUADRANGLE: APPLICATIONS TO LAND USE PLANNING AND RESOURCE MANAGEMENT

The Raleigh 1:100,000-scale (100K) quadrangle represents the culmination of over 10 years of geologic mapping by over a dozen geologists. All thirty-two 7.5-minute quadrangles that compose the Raleigh 100K have been mapped in detail as part of the U.S. Geological Survey’s STATEMAP and EDMAP programs. The map is a compilation of published and unpublished sources that is being field-checked and modified where necessary. The Raleigh 100K is located in an area of rapid economic and urban growth in the Piedmont of NC along the I-40 corridor. Increasing urban growth and development has emphasized the need for long-range land use planning and resource management, specifically groundwater resource management.

From west to east, the Raleigh 100K sheet includes a portion of the Late Triassic Durham basin, and portions of the Late Proterozoic to early Paleozoic Carolina, Crabtree, Falls Lake, Raleigh, and Spring Hope terranes. The center of the Raleigh 100K is dominated by the Pennsylvanian Rolesville granitoid batholith. The Carolina and Spring Hope terranes contain greenschist-facies metavolcanic and metasedimentary rocks. The Crabtree terrane contains amphibolite-facies felsic gneiss and pelitic schist. The Falls Lake terrane contains a heterogeneous assemblage of ultramafic to felsic and pelitic rocks overprinted with middle amphibolite facies assemblages. The Raleigh terrane contains amphibolite-facies polydeformed gneisses and schists.

The Raleigh 100K sheet will assist state, county, and local planners in identifying: 1) potential areas of elevated, naturally occurring dissolved metals in areas of sulfide mineralization, 2) potential high radon concentrations in groundwater, and 3) effective locations for future private and community wells. The NCGS and the Wake County have collaborated on a digital “Groundwater Atlas of Wake County, NC.” The digital atlas incorporates geologic layers from the Raleigh 100K sheet overlain with various water quality parameters collected from water supply wells throughout the county. This team effort has provided an informative map to Wake County staff that will enhance future planning decisions.