Geologic mapping of nebraska old rocks, new maps, fresh insights

Geologic mapping in Nebraska and environs is an ongoing endeavor that has spanned more than 170 years, involved dozens of scientists, and evolved through many changes. Digital mapping has risen to dominance in the state only since 1996. Geologic mapping in Nebraska today concentrates on surfi cial mapping, which emphasizes materials exposed at the land surface and their relationships with landforms, and which is particularly relevant because non-b edrock geologic materials (regolith) lie at the surface across at least 87% of the state. Moreover, surfi cial geologic maps assist the understanding of groundwater and sand and gravel resources, to name a few applications. Th e statewide bedrock map of Nebraska, which dates to 1986, remains an important and widely used geologic map, but it needs to be revised. Notwithstanding, when contemplated deeply, Nebraska’s statewide bedrock map reveals that (1) eff ects of gentle geologic structure, mainly those that came to be in the past 80 million years, can be discerned, and (2) some aspects of the map patterns (not the mapped sedimentary rocks per se) probably predate the beginning of the Pleistocene Epoch, about 2.6 million years ago. Th e geologic mapping of Nebraska, however, is far from completed.