We are told in this verse and by the events that happened in Alma 43:39-42 that the land of Manti was probably located on the west of the river Sidon and somewhat by the head waters of that river, and that at least some of the borders of the land of Manti and also the head of the river Sidon were probably located near or in an elevated (mountainous) strip of wilderness that represented the separation of the land of Zarahemla and the land of Nephi. [See the commentary on Alma 2:15]
According to David Palmer, the exposition of arguments for the one-Cumorah view in Doctrines of Salvation, includes several references to the march of Zion's Camp. Zion's Camp was an expedition led by Joseph Smith from Kirtland, Ohio, to western Missouri in 1834. During the march, one of the mounds observed was identified as the ". . . ancient site of the City of Manti, which is spoken of in the Book of Mormon. . ." This incident was cited to substantiate the idea of Book of Mormon cities in North America. Aside from the fact that such statements were completely unsubstantiated, it is instructive to consider that the idea appears unfeasible. There is only one City of Manti referred to in the Book of Mormon. It was by the "head of the river Sidon," which was near the strip of "wilderness" separating the Nephites from the Lamanites. (Alma 22:27) That strip . . . divided the land of Zarahemla from the land of Nephi. Both of those lands were southward from the narrow neck of land. [David A. Palmer, In Search of Cumorah, p. 74]
Geographical [Theory Map]: Alma 22:27 A Narrow Strip of Wilderness (4th Year)
Alma 22:27 A narrow strip of wilderness ([Illustration]): The Sierra Los Cuchumatanes mountain range in Guatemala is a formidable boundary running from the Bay of Honduras (the Caribbean Sea) on the east to the Sierra Madre range and the Pacific Ocean on the west. The rugged, steep Cuchumatanes soar over 10,000 feet above sea level. It is easy to visualize the similarities between this and the narrow strip of wilderness that separated the Nephites on the north from the Lamanites on the south. Only a few passes cross this range, all of which could have been strategic military defense positions for the Nephites. [Scot and Maurine Proctor, Light From the Dust, pp. 68-69]
Alma 22:27 The Borders of Manti and te Head of the [River Sidon] Fig. 17-3 Head of River Sidon, running from the east toward the west: borders of Manit.
Fig. 16-12 Hauck favors the Usumacinta river as the River Sidon: Allen and Sorensen propose the Grijalva River
Alma 22:27 Fig 17 5 [Lamanites] were spread through the wilderness. East by the seashore; Nephites nearly surrounded by Lamanites