Chase made these drawings after his second regression to the Civil War life to show what he saw in his memory. He was eight years old at the time. The commentary is Chase's too, describing what he saw, bad spelling and all.
We haven't tried to locate the valley that Chase described, but we do know that the hospital is a very accurate description of the make-shift hospitals set up near Civil War battles. And the "cannon" he described and drew is an accurate representation of a mortar. A Civil War historian pointed out to us that cannons were not roped down on wagons because they had their own wheels. But mortars always were.