The text does not indicate whether the "valley Alma" (Mosiah 24:20) was populated at the time of Alma's departure or was ever permanently settled. Perhaps it became a part of Lamanite lands, though with what name we are not told.
According to Joseph Allen, the Valley of Alma may be the crossroads in the highlands of Guatemala where a traveler can go in one of four directions. East takes you to Totonicapan, west carries you to Quetzaltenango, south leads to Guatemala City, and north is the road to Huehuetenango and on to the Mexican border. [Joseph L. Allen, Exploring the Lands of the Book of Mormon, p. 354]