Map of United States in the Middle Pennsylvanian Time
By Water Availability and Use Science Program
1969 (approx.)
![Map of the U.S. where most areas of the Nation are covered by sea and swamps.](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/full_width/public/thumbnails/image/USGSBulletin1291_mapofUS_MiddlePennTime.png?itok=hON-nsBB)
Detailed Description
Map of United States in Middle Pennsylvanian Time (about 300 million years ago). Source: USGS Bulletin 1291.
Sources/Usage
Public Domain.