According to Helaman 4:6-7, "the Nephites and the armies of Moronihah were driven even into the land of Bountiful; And there they did fortify against the Lamanites, from the west sea, even unto the east; it being a day's journey for a Nephite, on the line which they had fortified and stationed their armies to defend their north country. The reader should notice that these verses don't say "from the west sea, even to the east [sea]." An "east sea" is not directly mentioned. Therefore, we are left to wonder just how far this fortification line actually ran.
The Nephites fortified this line and stationed their armies "to defend their north country." We might wonder if this "north country" mentioned here as being defended by the Nephites is part of the same "north country" that Moroni later refers to in his writings? (Ether 1:1) Or is this "north country" just the lands northward from the fortification line? [Alan C. Miner, Personal Notes]
According to John Sorenson, perhaps this fortification line was more or less in the same sector centuries later called the land of Joshua (Mormon 2:6), which the Nephites occupied during their series of final battles leading up to the battle at the hill Cumorah.