I'm a huge fan of http://historicalmaps.arcgis.com/usgs/ http://historicalmaps.arcgis.com/usgs/ for finding USGS maps - it's a simple, visual browser to find al

I'm a huge fan of http://historicalmaps.arcgis.com/usgs/ http://historicalmaps.arcgis.com/usgs/ for finding USGS maps - it's a simple, visual browser to find all available years + scale levels for any location.