The hill Riplah is mentioned only in Alma 43. When the Zoramite/Lamanite army sees the strength and protection of the Nephite army, they "departed out of the land of Antionum into the wilderness, and took 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" (22). The Zoramite/Lamanite army does not plan to attack the city of Manti, which is a Nephite fortress, but to move first against "the weaker part of the people" (24).
Moroni sent spies to watch the Zoramite/Lamanite camp, and also sent delegates to Alma to ask "whither they should go to defend themselves against the Lamanites" (23). In response to the information from Alma, Moroni took a part of his army “over into the land of Manti” (27). To add to his army, Moroni "caused that all the people in that quarter of the land should gather themselves together to battle against the Lamanites" (26). The Zoramite/Lamanite army does not know Moroni is on to their plan and is not in a hurry to execute its plan to invade Manti, as these activities by Moroni would have occupied several days at least.
From Mormon's description of Moroni's strategy, we know that the river Sidon passes through a valley. Moroni secretes a portion of his army in this valley on the west side of the Sidon (27, 32), and Lehi takes a portion "over into the valley, and concealed them on the east, and on the south of the hill Riplah" (31). Furthermore, the portion of the valley in Manti, on the west side of the Sidon, is uninhabited, as Mormon refers to it as "wilderness" (27).
The hill Riplah could be located anywhere along Sidon's upper course where it forms Manti's southern border, but further identification is not possible unless an on-site survey can identify the valley with some certainty. The Action Map assumes a location only for the sake of demonstrating the action.
If we had no winter, the spring would not be so pleasant; if we did not sometimes taste of adversity, prosperity would not be so welcome. Anne Bradstreet
And if men come unto me I will show unto them their weakness. I give unto men weakness that they may be humble; and my grace is sufficient for all men that humble themselves before me; for if they humble themselves before me, and have faith in me, then will I make weak things become strong unto them. Ether 12:27
Yea, all things which come of the earth, in the season therof, are made for the benefit and the use of man, both to please the eye and to gladden the heart; Yea, for food and for raiment, for taste and for smell, to strengthen the body and to enliven the soul. And it pleaseth God that he hath given all these things unto man; for unto this end were they made to be used, with judgment, not to excess, neither by extortion. D&C 59:18-20