Whitfield's section of the narrative begins with his account of the night he spent "wrestling with Satan" (177). The only clue we have to the earthly location of this struggle is that it lies on the far side of the river from the Bundrens' house. Our decision to set it in the church where he is the preacher in the short story "Shingles for the Lord" is speculative.
This location represents the place between Armstid's farm and Mottson where Cash's leg is bothering him so much that even Anse concedes they will need to get some medicine when they reach the town. It is not one of the roads that Faulkner himself drew on either of his maps - and in fact it's incompatible with the layout of Yoknapatawpha on either map. Like so much of the landscape in As I Lay Dying we have to speculate about where to plot the road on our map of the events in the novel.