The Land Desolation was exclusively in the Land Northward. Indeed, it was used as the name for the the Land Northward:
Thus the land on the northward was called Desolation, and the land on the southward was called Bountiful (Alma 22:31)
The two lands were separated by a Narrow Passage:
And it came to pass that I did cause my people that they should gather themselves together at the land Desolation to a city which was in the borders by the narrow pass which led into the land southward. (Mormon 3:5)
Any modeler who places the Land Desolation or parts thereof south of the Narrow Passage do so contrary to scripture.
The following verse shows how parallel the lands Bountiful and Desolation were:
And now 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 (Alma 22:32)
**Both lands, i.e. Bountiful and Desolation stretched from the West Sea to the East Sea.**
This “line” was a flat plain which remained as the Sea that Divides the Land shrunk (Currently called Ancient Lake Tonawanda). You could see Desolation from Bountiful thus the expression “Sea that Divides the Land” like a mud puddle divides a road or trail.