I found this bit of map in a set of encyclopedias I bought used (not a part of the books, more like a piece of paper someone put to mark a place).
It’s a contour map. The east-west grid lines are marked (top-to-bottom) 84, 83, 82, 81
Otaki-yama at the very bottom.
Just above that ‘Yokokawa Imperial For’ (cut-off)
Crossing from NE to SW is a ridge line marking, with peaks marked at 1725, 1782 and 1862.
In the NW corner, a river, road and railroad cross, also from NE to SW, and all in the same narrow valley. In the middle of this valley is a town marked Hirosawa
I’ve googled for Hirosawa, Yokakawa, and Kawashima, but haven’t turned up anything definitive.