USGS map of Grand Canyon--who wants it?
If there is a more appropriate forum, please let me know.
I have a Geological Survey map of the Grand Canyon. It advertises itself thusly.
Grand Canyon National Park and Vicinity
N3600 W11145/28x60
1962
The southeast corner of the map is marked 36°00' and 111°45'; the northwest corner is marked 36°28' and 112°45'. This leads me to conclude that 28x60 denotes the size of the area shown on the map in minutes. The paper map is about 38x59 inches, so it's not something you would while driving (I hope).
What else can I tell you? I was about to throw it out and it occurred to me that someone might want it.