USGS Maps in Google Maps Gallery

USGS Topo Maps in Google Maps Gallery

Over 193,000 Topo  Maps georeferenced in a seamless USGS Layer with a transparency control on the left.

See the Maps
http://maps.google.com/gallery/details?id=z4f-ZuCLmiKg.kUOos96GzVzs&hl=en

source:
http://googleenterprise.blogspot.com/2014/03/us-geological-survey-and-google-maps.html