Welcome to Mississippi! What unit was your ancestor in?
Does anyone really know the positions of the units at these battles? I love Grabau's "98 Days," and the maps are best in any ACW book ever ... but his placement of the units on the maps is approximated to several hundred yards and never seems to jive with what the soldiers are describing.
Personally, I'm a terrain junkie. I like to know what caused a particular unit to stop in its tracks, or change facing, or wheel to the left. Take, for instance, the report of the 1st Missouri Cavalry:
"We drove the enemy about a half or three-quarters of a mile through a corn-field and across some deep ravines before they brought us to a stand. This was under a desperate fire. They occupied one ridge and I another, with a deep, narrow ravine between us. There they shot my horse three times, and he lay down and died like a soldier. Three times I tried to drive them from their position, but my men were not able to ascend the hill on which the enemy's line was formed."
If you look at the map at the link below, this ravine is near the red number 29. To view the ravine first-hand is even more daunting.
On the opposite side of the Jackson Road, several batteries of artillery were facing up the hill into the gap between Boomer and Holmes. A lot has been made out of the fact that the wagon trains had been mistakenly ordered away, but Cockrell's charge was terminated by terrain and force of arms, not supply issues. I have yet to see a Vicksburg Campaign history take note of this ravine, or pinpoint the location of the batteries facing up the hill.
I think if this type of stuff was irrelevant to the veterans themselves, they wouldn't have gotten together 50 years later to mark the exact lines of fortifications in Vicksburg.