http://adventure-journal.com/2016/08/you-can-now-get-every-u-s-topo-map-for-free-easily/ (http://adventure-journal.com/2016/08/you-can-now-get-every-u-s-topo-map-for-free-easily/)
http://www.natgeomaps.com/trail-maps/pdf-quads (http://www.natgeomaps.com/trail-maps/pdf-quads)
Resolution isn't quite what I'd call excellent.