US Topo maps have a credit legend in the lower left-hand corner of the map collar. This includes a short summary of data sources and data currency.
More detailed source information is in an XML metadata file attached to each GeoPDF file. This file contains series-level, quad-level, and layer-level metadata, but US Topo does not preserve or track feature-level metadata. Open the GeoPDF map file in Acrobat Reader and click on the paperclip icon to access the metadata file (a US Topo Map Symbols file is also attached).
Two metadata XML documents—one for the map and one for the orthoimage—are included with GeoTIFF files downloaded from TopoView.