The foundation of both lithic provenance and prehistoric quarry studies lies in the construction of fine-scale geological base maps. The U.S. Geological Survey and the individual state surveys have compiled geologic maps of the entire country, but these maps are typically at a resolution (1:24,000 or lower) that lacks sufficient detail for a given archaeological investigation. Moreover, bedrock descriptions that are useful to geologists frequently do not include the sort of lithic resource information an archaeologist would like. For example, cherts are notoriously neglected in bedrock descriptions.

To compensate for this lack of detail, La Porta & Associates combines fundamental geological methods with GPS survey techniques to produce our own detailed bedrock geological base maps. These maps include key bedrock formation boundaries and markers beds, of course, but they also include various structural data (joint sets, cleavage, bedding planes and fault surfaces), which are particularly useful for prehistoric quarry predictive models. These same structural and stratigraphic data can also be used (via geometric construction) to complete maps in areas where dense vegetation or modern land usage may make a complete walkover difficult. All geologic data are compiled into GIS-compatible map form.