To learn more about geologic maps, see:
U.S. Geological Survey (USGS)
USGS/AASG National Geologic Map Database
USGS’s Geologic Maps of the U.S. States
A Tapestry of Time and Terrain
Database of the Geologic Map of North America
USGS’s Geology of the Conterminous U.S.
Paleontology Portal’s Tapestry of Time Teacher’s Guide
National Cooperative Geologic Mapping Program (NCGMP)
USGS EDMAP Program - Training the Next Generation of Geoscientists
American Association of State Geologists (AASG)
Find Your State's Geologic Map Here
National Park Service (NPS)
NPS Geologic Resources Inventory
National Aeronautics and Space Administration (NASA)
American Geosciences Institute (AGI)
AGI’s Meeting Challenges with Geologic Maps
Additional:
Look for Geologic Map Day on Facebook and Twitter!