My parents visited Champion's Hill a couple decades ago. They were told that our ancestor (Bluford Barton "B.B." Williams) was most likely buried in a mass grave, as you said. There was no record of his burial.

My brother and I plan to visit this summer. We don't expect to find a grave, but we want to walk the ground. Plus, as Civil War history buffs, we plan to trace Grant's entire campaign. Good ideas appreciated!