The south wilderness was a region on the east side of the river Sidon, beyond the borders of the land of Manti, marking the southern frontier between Nephite and Lamanite lands.
When Lamanite raiders carried off Nephite captives, Alma inquired of the Lord and learned that the Lamanites would cross the Sidon into the south wilderness, beyond Manti. Zoram and his sons crossed the river with their armies, met the Lamanites on the east side of the Sidon, and recovered the captives (Alma 16:6-7).
The wilderness was filled with wild animals of every kind, some of which had come from the land northward for food. It lay in the land called Bountiful, to the south, while the land northward was called Desolation (Alma 22:31).
The Zoramite land of Antionum, east of Zarahemla and south of Jershon, bordered this wilderness on its south side; the wilderness itself was full of Lamanites (Alma 31:3).
Moroni sent his armies into the east wilderness and drove the Lamanites there back into their own lands south of Zarahemla, then resettled Nephites in the cleared territory and fortified the frontier (Alma 50:7).
In the closing campaigns of the war, Moroni, Lehi, and Teancum encamped their armies around the land of Moroni, encircling the Lamanites in the borders by the wilderness on the south and on the east (Alma 62:34).