There are several sets of scriptural references that help in triangulating the location of the head of the river Sidon relative to Book of Mormon cities and lands.

Mormon indicates the dividing line separating the Nephite lands from the Lamanite lands extended “through the borders of Manti, by the head of the river Sidon” (Alma 22:27). This description places the head of the river Sidon near the borders of Manti. It is not clear if the head of the river Sidon is within the borders of Manti, or simply the borders of Manti are “by the head of the river Sidon.” The land of Manti appears to be the most southern fortified region of the Nephites, because it was often attacked first when the Lamanites approached the Nephite lands from the south wilderness. There is clear evidence the Nephites—nearly surrounded by the Lamanites—set up defense cities as early warning positions near the borders of the land of Zarahemla (Alma 22:28–29). These cities included Manti to the south (Alma 16:6–7; 17:1), Minon to the east (Alma 2:24; 6:7) and possibly Melek to the west (Alma 8:3; 35:13).

In the commencement of “the eighteenth year the people of the Nephites saw that the Lamanites were coming upon them; therefore they made preparations for war; yea, they gathered together their armies in the land of Jershon.” The “Lamanites came with their thousands; and they came into the land of Antionum, which is the land of the Zoramites; and a man by the name of Zerahemnah was their leader” (Alma 43:4–5). The Nephites “knew the extreme hatred of the Lamanites towards their [Lamanite] brethren, who were the people of Anti-Nephi-Lehi, who were called the people of Ammon—and they would not take up arms, yea, they had entered into a covenant and they would not break it—therefore, if they should fall into the hands of the Lamanites they would be destroyed. And the Nephites would not suffer they should be destroyed; therefore they gave them lands [the land of Jershon] for their inheritance” (Alma 43:11–12). Moroni, the “man who had been appointed to be the chief captain over the Nephites, … met the Lamanites in the borders of Jershon,” after he had “prepared his people with breastplates and with arm-shields, yea, and also shields to defend their heads, and also they were dressed with thick clothing.” The “army of Zerahemnah was not prepared with any such thing; they had only their swords and their cimeters, their bows and their arrows, their stones and their slings” (Alma 43:16, 18–20). The Lamanites “were not armed with breastplates, nor shields—therefore, they were exceedingly afraid of the armies of the Nephites because of their armor, notwithstanding their number being so much greater than the Nephites” (Alma 43:21). As a consequence, the Lamanite army retreated from the borders of Jershon towards the land of Manti:

In this military travel sequence, the Lamanites under the command of Zerahemnah retreated from the borders of Jershon and the land of Antionum to the northeast of the land of Zarahemla and continued “round about in the wilderness, away by the head of the river Sidon, that they might come into the land of Manti and take possession of the land”. Note the journey went “away by the head of the river Sidon, that they might come into the land of Manti” (Alma 43:22). After the Lamanites had gone around the head of the river Sidon, but before they were able to reach the land of Manti, they unexpectedly encountered captain Moroni and his Nephite army at hill Riplah on the east of the river Sidon (Alma 43:34–40). The Lord through Alma the prophet had informed Moroni of the travel plans of the Lamanite army which included, “marching round about in the wilderness [after leaving the borders of Jershon and the land of Antionum], that they might come over into the land of Manti, that they might commence an attack upon the weaker part of the people” (Alma 43:24). In preparation, captain Moroni placed his army to the west, south and east of hill Riplah, knowing the Lamanite army would need to pass on the north of the hill Riplah when taking “their journey round about in the wilderness, away by the head of the river Sidon, that they might come into the land of Manti and take possession of the land; for [the Lamanites] did not suppose that the armies of Moroni would know whither they had gone” (Alma 43:22; see also, Alma 43:3–54). When the Lamanites passed on the north of “hill Riplah, and came into the valley, and began to cross the river Sidon, the army which was concealed on the south of the hill, which was led by a man whose name was Lehi, and he led his army forth and encircled the Lamanites about on the east in their rear” (Alma 43:35). This encirclement of the Lamanites “on the east in their rear,” by Lehi’s forces, “concealed on the south of the hill,” would only align if the Lamanites were approaching hill Riplah on the north from a northeast direction.

This travel route of the Lamanite army from the northeast, by way of the head of the river Sidon, and advancing to hill Riplah, positions the head of the river Sidon north of the land of Manti, between the borders of Jershon to the northeast of the city of Zarahemla, and the land of Manti to the south of the city of Zarahemla (see also, Northeast in the section, A Directional Flow of the River Sidon, above, and Hill Manti in the section, Hills, Valleys and Banks, below).

Another military travel sequence helps triangulate the location of the head of the river Sidon. Captain Moroni received an epistle from Helaman, reporting “in the twenty and sixth year” the Lamanites had “obtained possession by the shedding of the blood,” the “land of Manti, or the city of Manti, and the city of Zeezrom, and the city of Cumeni, and the city of Antiparah” (Alma 56:1, 9, 13–14). The Lamanites maintained possession of “those cities which they had taken” to the south of the city of Zarahemla (Alma 56:20). In the next year, the Nephites prepared themselves and their other cities for defense, so the Lamanites could not “make an attack upon them in their strongholds,” and “to make an attack upon [their] other cities which were on the northward” (Alma 56:21–22). As a result of these Nephite defense preparations in their cities to the north,

The places mentioned in these verses—the city of Zarahemla, the head of Sidon and the city of Nephihah—show a military travel sequence the Lamanite army would have taken when coming from the south to attack other Nephite “cities which were on the northward” (Alma 56:22). The record states that if the Lamanites had followed this route, they would have marched from their locations on the south and west of the city of Zarahemla—where they had already taken the land of Manti and the cities of Manti, Zeezrom, Cumeni and Antiparah—northward to the city of Zarahemla and then to a place where they would have crossed the head of Sidon as they continued their march over to the city of Nephihah on the east of the city of Zarahemla (Alma 56:13–26; see also, Alma 50:14; 51:24–26; 59:5; 62:30). This travel sequence places the head of the river Sidon to the east of the city of Zarahemla and northward of the land of Manti and the captured cities of Manti, Zeezrom, Cumeni and Antiparah. These last three cities were on the west of the city of Zarahemla, and the city and land of Manti were on the south. Thus the Lamanites, while occupying and holding these southern cities, dared not pursue a route that would have taken them north to attack the “sufficiently strong” city of Zarahemla, and then to cross the head of the river Sidon before continuing over to the city of Nephihah on the east (Alma 56:23).

Triangulating and combining these two sets of relative directions, based on military journeys, positions the head of the river Sidon between the land of Manti, and the land of Jershon, and also directly to the east of Zarahemla, between the city of Zarahemla and the city of Nephihah. The head of the Rio San Ignacio in Baja California, situated between these lands and cities, accurately matches the alignment of the geographical descriptions in the Book of Mormon account.

Mormon states the water at the head of the river Sidon is “running from the east towards the west” (Alma 22:27). In a contrasting orientation, the text also consistently indicates the main course of the river has lands and cities and physical features on its west and on its east (on the west, Alma 2:34; 8:3; 43:27, 32, 53; on the east, Alma 2:15, 17; 6:7; 16:6–7; 43:53; 49:16). This requires the river at these points to be flowing in a general south direction to meet this east and west orientation and to position the head (or source) of the river on the north of the land of Manti as outlined above. Then in still another change in course, the river at its mouth could only empty into the one available sea—the sea west—by flowing in a westerly direction from its watershed divide. These three required orientations and directions are at ninety degrees to each other. Somewhere there has to be a bend in the river Sidon, a change in direction, to match and at the same time smooth these three abrupt segments of its route: first east to west, then north to south and finally east to west. We suggest the only natural and moderate flow pattern that would match all of these conditions required by the Book of Mormon account is for the flow at the river’s head to start from east to west and then the main course, somewhere near its head, to bend slightly before flowing in a southwest direction to the west sea. This would allow the water at the head to flow correctly, the lands and cities and physical features along its course to still be positioned on the east and on the west—including the south wilderness—and for the river to ultimately reach a western sea. A bend and change of direction occurs near the head of the Rio San Ignacio in Baja California, allowing the river to match all the required conditions and orientations.