If You've ever been to the Cedar Forests in Northern Montana and Idaho you would know how utterly impossible it would have been for an Army to move through, not only are the trees monstrous (about RTW Sized), but the undergrowth snags you every couple of feet, coupled with the fact that you can only visibly see maybe 20-50m ahead of you at any given time, its no small wonder why somebody could get lost so easily. In Fact, every so often hikers will still find the remains of people who died there from getting lost several years previous. I imagine it would be a great place to hide a body