It is not an erosional remnant. If one used this criteria to place unconformities, then unconformities could be found at every lithological boundary that separates formations. His reason prevailed but such was not the case with the Knox Unconformity. There is only one unconformity that separates the Sauk Sequence from the overlying Sequence. That this real unconformity could be relegated to a trash bin and deemed unimportant does violence to all we know about geology.
Morrow County is unique in that a special set of circumstances came together.
North and northeast from Morrow County the Cambrian rocks that formed the unique type of porosity found in Morrow County disappear. Unless one is an ideologue, it is not difficult to see in cross-sections that the trap rock in Morrow County, above the unconformity, is primarily a function of facies changes. When the Cambro-Ordovician boundary is properly recognized it becomes evident that the Morrow County trap rock system developed both above and below this unconformity. Elsewhere, this straddling of the unconformity changes to trap development either above or below. Examples of this abound in this research.