According to Mormon 1:3-5, when Mormon (then 10 years old) turned 24 years of age, he was to "go to the land Antum, unto a hill which shall be called Shim." He was to "take the plates of Nephi unto [himself]" and "engrave the things concerning this people." It is significant that here in verse 5, Mormon says that "I remembered the things which Ammaron commanded me." When Mormon turned 24 it would have been 335 A.S. (compare 4 Nephi 1:48, Mormon 1:2). The last recorded episodes of Mormon before 335 A.S. were "in the three hundred and twenty and seventh year" (Mormon 2:3) when the Lamanites drove the Nephite armies from the city of Angola and the land of David until they came to the land of Joshua, "which was in the borders west by the seashore" (Mormon 2:6).
Mormon records that in the land of Joshua, the Nephites withstood the Lamanite armies "and three hundred and thirty years had passed away" (Mormon 2:9). In the land of Joshua, the Nephites began to repent and apparently maintained their position for about 14 years (Mormon's next date is recorded "in the three hundred and forty and fifth year" when "the Nephites did begin to flee before the Lamanites" (Mormon 2:16). It seems odd for Mormon not to mention more details of any trip to the hill Shim during this 14-year time period. I have to ask myself why this trip is not mentioned until ten years later? (Mormon 2:16-18) The reader should note that if we were to plot Mormon's travels according to the hemispheric geographical model (North America-South America), this round trip from a South America location south of the narrow neck (Panama) to a proposed hill Shim situated somewhere near the state of New York could have taken Mormon up to 6000 miles.
Assuming a Mesoamerican setting, Mormon's probable route to the hill Shim would have taken him from a location near the "west" coast on the Pacific Ocean through the Isthmus of Tehuantepec. Depending on the Mesoamerican geographical theory, this distance to the proposed hill Shim would range from just a few miles to a little over one hundred. I would have to suppose that during Mormon's trip to the hill Shim, Mormon's army would have been stationed "in the borders west by the seashore" blocking the Lamanite advance. [Alan C. Miner, Personal Notes] [See Geographical Theory Maps]
Geographical [Theory Map]: Mormon 2:10-15 [No Record] Mormon Goes to Hill Shim and Retrieves Plates ("335 A.S.")