Introduction

In the early 1800s, state and federal geological survey agencies were conceived to address increasing demands for natural resource information to fuel the Industrial Revolution. More recent urbanization, however, has spurred surveys, along with their university and industry partners, to extend their applications from mining and energy to water supply, engineering, hazards, environment, and climate change, while more directly supporting the needs of decision makers.
Geological maps are at the heart of this decision support system. They are the method geologists use to synthesize and communicate an understanding of earth materials, processes, and history; however, for all geologic mapping, challenges remain in obtaining the information required to construct maps that are meaningful and helpful to users. This is particularly acute for subsurface mapping. Geologists must process data obtained through field work, geophysical surveys, and laboratory analyses and then compile that data to map the composition and distribution of materials in a format and resolution that serves map users. In turn, map users have an obligation to grasp the uncertainty of the map while providing the best possible service to their clients.

Previously, technological and data limitations dictated that a two-dimensional (2-D) paper map—accompanied by at most a few cross sections and a report—was the most appropriate publication format, so users were expected to infer subsurface conditions at their site. Over the past two decades, however, in response to demands for subsurface information in extensive areas of thick sediments and sedimentary rocks, 2-D geological mapping has been superseded by three-dimensional (3-D) mapping. Geological mapping thus has been redefined in these settings—from a single-layer 2-D map to a 3-D model showing thickness and properties of multiple stacked layers (Turner, 2003; Culshaw, 2006).

Having thus raised expectations among users for 3-D mapping, surveys and their partners are now seeking to rapidly improve their methods for construction, dissemination, and use of 3-D geological maps to support decision makers who must balance economic growth with environmental protection.

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Manuscript received 3 Jan. 2010; accepted 17 May 2010

doi: 10.1130/GSATG86GW.1