Jashon was a Nephite land and city south of the land of Shem. In the 345th year (AD 345), the Nephites fled before the Lamanites and were pursued to the land of Jashon before they could halt their retreat (Mormon 2:16). The city of Jashon stood near the place where Ammaron had deposited the Nephite records to keep them from being destroyed; Ammaron had directed that they be hidden in the land Antum, in a hill to be called Shim (Mormon 1:3; 2:17).
Ammaron had instructed Mormon, a descendant of Nephi, to go at the age of twenty-four and take the plates of Nephi while leaving the rest in place (Mormon 1:4; 2:17). Mormon recorded that he had done so, taking the plates of Nephi and continuing the record according to Ammaron’s word, which occurred in AD 346 (Mormon 2:17, 20). The Nephites were then driven northward from Jashon to the land of Shem (Mormon 2:20).