Urban Geologic Mapping - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 168

There are several sources of information in urban regions useful for geological pur-
poses, which, in some cases, may be more extensive than what is available for mapping
undeveloped regions. Often, to be successful in gathering information on the geology
of urban areas, the geologist must become a forensic geologist, because the near-surface
unconsolidated deposits in many urban areas of the United States have experienced sig-
nificant disturbance. Being a forensic geologist means knowing and evaluating whether
the information collected is reliable and valid and whether it should be included in the
final urban geologic map.
Mapping the geology of an urban region begins with a literature review of existing data
and publications using the following sources as a guide:
• Current and historical maps:
• Geologic maps
• Planning maps
• Historical highway maps
• Fire protection maps (often referred to as “Sanborn maps”)
• Topographic maps (7.5 min scale is best)
• Trail maps
• Historical interest maps
• Park and recreational maps
• Maps prepared for site-planning purposes; these often contain accurate loca-
tions of existing underground infrastructure and above-ground water man-
agement structures, such as detention basins
• Others
• United States Geological Survey studies and reports
• State Geological Survey studies and reports
• State and local water well records
• Army Corps of Engineers reports and studies
• Oil and gas records, studies, and reports
• Department of transportation studies and reports
• Building construction reports and permits
• Geotechnical reports and studies
• State and local environmental investigation reports and studies at sites of
contamination
• State and local historical societies studies; publications, and photographs
• State and local universities and colleges
• Sources of historical aerial photographs
• Previously published scientific literature
You may think historical highway maps cannot provide valuable information to help
understand the geology of a particular area or region—but this is simply not true. Old and
even new highway maps provide valuable information on mapping the geology of urban
areas (Bennison 1974).