If rifting in the North American Midcontinent reflects early Flood processes, then defining the thickness and distribution of the total diluvial record requires mapping the base of these rifts. Using publicly available data, we created a 3D map of the base of the largest, the Midcontinent Rift. Combined with similar maps of the East Continent Basin, the Reelfoot Rift-Rough Creek Graben, and Rome Trough, we propose a basal diluvial boundary for the upper Midcontinent Region. The scale of the rifting is seen in the volume of fill; rift fill comprises well more than half of the total diluvial volume. Despite significant erosion, the rifts remain as stunning reminders of crustal disruption at the onset of the Flood, revealing significant geological activity—structural, erosional, volcanic, intrusive, and depositional—before the transgressive marine front of the Flood. Using these maps, quantitative estimates of all of the Flood and Ice Age rock records can be estimated, providing a solid basis for forensic interpretation.