The Internet provides access to a variety of information, but not all of it is accurate, reliable or current. The websites listed below are maintained by reputable organizations and contain trustworthy information.
U.S. Geological Survey (USGS)
Pennsylvania Geological Survey (also called the Bureau of Topographic & Geologic Survey)
Crystal Cave Park -- Kutztown, PA
Delaware Water Gap National Recreation Area -- Stroudsburg, PA
Hickory Run State Park -- Carbon County, PA
Lackawanna Coal Mine Tour -- Scranton, PA
Lost River Caverns -- Hellertown, PA
"Trail of Geology" guides, published by the Pennsylvania Geological Survey, describe the rock formations you can see at various state parks across the Commonwealth.