Dear Mr. Arnaud,
I believe those maps are probably aerial photos that were taken by the U.S. Geological Survey. They would then send those photos to their mapping department - they would create the updated 'topographic' maps from those photos. The USGS at one time printed a map of each state that showed the 7.5 grid lines, and users could use that map to locate the part of the state they were interested in, and what 7.5 topo maps covered that area. They also had an alphabetical list of all the topo maps for each state. I would suggest contacting the USGS Library (
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