Fall Line
Map if from USGS website showing what geologist call the Fall Line Zone. This zone separates the Coastal Plains of Virginia, Delaware and Maryland from the hard bedrock of the Piedmont. Above the Piedmont are the Appalachian Mountains. This fits the description found in 3 Nephi 4:1 where robber armies came down from the hills and mountains.
In Alma 22:32 it reads “it was only the distance of a day and a half’s journey for a Nephite, on the line Bountiful and the land Desolation, from the east to the west sea.”
Above the Delmarva peninsula is a change in geologically features geologists call the “fall line.” From the Susquehanna river to the Delaware river, the fall line is approximately 35-40 miles, a reasonable distance for a “day and a half’s journey.” The land of Desolation borders the land of Bountiful and is located in the land “northward.” Desolation, therefore, is above the fall line in the Piedmont region.
The fall line continues on the west side of the Susquehanna river and below that is the land of Zarahemla. The land of Bountiful, the land of Nephi and the land of Zarahemla were all in the land southward, which is located on the "coastal plain" section of the map above.