MISSISSIPPI RIVER ALLUVIAL GEOLOGY AND THE VICKSBURG CAMPAIGN

The final phase of MG U.S.Grant's Vicksburg Campaign began 31 Mar 1863 as his XIII Corps left Millikin's Bend, LA, for New Carthage, LA. At New Carthage, Grant hoped to cross the River onto Mississippi high ground and operate against Vicksburg. Some accounts intimate Grant's force moved directly south. Actually, the ancestral meander and natural levee geology of the Mississippi Alluvial Plain dictated a circuitous route and prevented interdiction by Confederates further west. Since the last glaciation, the River has meandered across its flood plain, abandoning numerous channels. Many channels formed Bayous, the principal drainages of the area. When these channels were active, sedimentation during floods built natural levees up to ten feet above the surrounding area. In the 19th century, the only roads were along the natural levees since they were last to be flooded. Beyond the natural levees lay backswamp deposits-low areas that take months to drain after floods. Federal forces took the Walnut Bayou natural levee road, and after a skirmish at Richmond, LA, proceeded south on the natural levee road west of Roundaway Bayou. By 3 Apr, they were near New Carthage, but finding it flooded, moved to Ione's Plantation, where about 20 acres of dry ground was located. This was fine for most of the XIII Corps, but not enough for most of the Army, soon to follow. Here, pursuit of Confederate snipers revealed that the backswamp to the west was completely flooded, protecting the Federal troops from attack. Reconnaissance revealed that a road on the west side of Bayou Vidal extended almost to a road on the west side of Lake St. Joseph. Both roads were on natural levees and eventually led to an open, flat, dry area near Hard Times Landing, LA, on the River. On 16 Apr, several Union ships ran past the Vicksburg batteries and joined Grant's army. By 27 Apr 1863, two-thirds of Grant's army was near Hard Times. The Geology of the Alluvial Plain had forced, but permitted, the Army to march almost 60 miles to advance 25 miles downriver. Grant now had soldiers south of Vicksburg and boats to transport them across the Mississippi. Grant had only to strike!