Since the late 1800's, the U.S. Geological Survey has been responsible for maintaining a lexicon of geologic names for the Nation, including brief definitions for each unit (e.g., the lithology, thickness, age, underlying and overlying formations, and type locality). These lexicons are searchable through Geolex, which is a subset of the National Geologic Map Database. Geolex consists of stratigraphic names from around the United States, and includes reference histories for units, preferred names, and updated names.
Search by unit name (or portion of name!), or click through the interactive map search function. Links to additional Stratigraphic Resources are included as well.
"Grand Canyon National Park: Yavapai Geology Museum 0453" by Grand Canyon NPS is licensed under CC BY 2.0
