16.1: What Are Geologic Maps and Why Are They Important?

What Are Geologic Maps and Why Are They Important?

A geologic map Links to an external site. uses lines, symbols, and colors to illustrate information about the nature and distribution of rock units within an area (Figure 16.1). Typically, a geologic map will depict mappable rock or sediment units. A mappable unit of rock or sediment is one that a geologist can consistently recognize, trace across a landscape, and describe so that other geologists may recognize and verify its presence and identity. Generally, a mappable unit is a geologic formation Links to an external site.. These mappable units are shown as different colors or patterns on a base map (usually a topographic map Links to an external site.), over which information about geologic contacts and strikes and dips are included. Geologists make these maps by making careful field observations at numerous outcrops Links to an external site. (exposed rocks at the Earth’s surface) throughout the mapping area. At each outcrop, geologists record information such as rock type, strike and dip of the rock layers, and relative age data. Geologic maps take practice to understand, since they display three-dimensional features, such as folds, on a two-dimensional surface. 

Geologic maps are important for two reasons. First, as geologists make geologic maps and related explanations and cross-sections, they develop a theoretical understanding of the geology and geologic history of a given area. Second, geologic maps are essential tools for practical applications such as zoning, engineering, and hazard assessment. Geologic maps are also vital in finding and developing geological resources, such as sediments, groundwater, fossil fuels, and minerals.