Geographical: Sorenson notes some of the factors surrounding his suggestion that the site of Santa Rosa along the Grijalva is a candidate for the location of Zarahemla:
"The largest archaeological site on the upper Grijalva in an appropriate position to qualify as Zarahemla is Santa Rosa…By 1974 the site had been inundated by waters backed up nearly 70 miles behind Angostura Dam…
Linguistic research tells us that the upper Grijalva lay at the juncture of two major areas where long-established peoples and their languages existed. A couple of thousand years ago the Mayan languages probably extended throughout much of Guatemala to about the mountainous wilderness strip that separates the highlands of that nation from the Grijalva River valley. Downstream, from near Chiapa de Corzo and extending north and westward, were speakers of Zoque dialects; in the isthmus proper was the closely related Mixe language. Both blocs, the Mayan speakers on the Guatemalan and groups using tongues of the Mixe-Zoquean family on the isthmian side of Santa Rosa, had been there a long time. Ancestral Mixe-Zoquean has been shown to be the probable language of the Olmecs of the Gulf Coast, while Mayan speakers likely had been in the Cuchumatanes Mountains of Guatemala since well before 1000 B.C. (Evidence is uncertain, however, whether Mayan languages were spoken until post-Book of Mormon times in the actual areas of the southern Guatemalan highlands where the Nephite and Lamanite settlements are best placed.) But neither major language group seems to have been established on the upper Grijalva, at least not until well into A.D. times. That intermediate zone seems to have been a linguistic frontier. Zarahemla's people had moved into the area from the Gulf Coast through lands occupied by Zoque speakers for centuries. His local followers in Mosiah's day likely spoke a language like Zoquean. Mosiah and his party, coming from the opposite direction, were among the first of a long series of groups who drifted down out of Guatemala into this valley over the next thousand years.
The archaeological sequence at Santa Rosa is interesting in terms of the Book of Mormon, although the findings will always remain incomplete because the site is now underwater. Major public construction in the form of what seem to have been "temple" or "palace" foundation mounds started on a modest scale at approximately 300 B.C. That coincided with growth in population, which produced the "city" of Zarahemla that Mosiah's party encountered a couple of generations later. The place remained no larger than a modest town, as we think of size, during the time when Mosiah, Benjamin his son, and Mosiah II reigned. Around 100 B.C. a spurt in the city's prosperity is evident, and a large number of major public structures were erected. That condition continued for around a century. Except for the site of Chiapa de Corzo far downstream, Santa Rosa became the largest, most significant "city" in the Grijalva basin just at the time when Zarahemla is reported by the Book of Mormon as becoming a regional center. (Sorenson 1985, pp. 153-155).
As Sorenson points out, an interesting complex of factors comes to bear on Santa Rosa as a potential site for Zarahemla. The archaeological indication of a population explosion right at the time we have Mosiah and his people entering the city is quite suggestive. While the linguistic data do not tell us much at the moment, the position of Zarahemla along a linguistic, probably cultural frontier will have decided impact on our understanding of some of the events later discussed for Zarahemla.
Sociological: Most fascinating is the reception that Mosiah's people receive as they enter Zarahemla. They are met with rejoicing. This is most interesting if we remember that Mosiah's people have been struggling through the wilderness for forty or more days. They certainly would not have been able to present themselves as a royal procession. They most certainly would have been bedraggled, and in need of the food and rest of a city.
How is it that there was rejoicing when Mosiah arrived? Part of our problem is that we are getting this history from Amaleki long after their arrival. The story is slightly disjointed, because we rejoicing from the beginning, and apparent knowledge of genealogy, but this does not actually occur until later, as noted in verse 18. From that future perspective looking back on the past, the important part was the rejoicing, and Amaleki does not take care to mention whether the rejoicing occurred immediately or sometime after their arrival.
I would suggest that the standard processes of strangers meeting would dictate that the rejoicing was not immediate. First there would have been some determination that Mosiah and his people were not a military patrol. They might then have been welcomed and fed. It is during the process of exchanging information so that they might know how to treat each other that the rejoicing occurs. From the brief text, we may suppose that the thing that keyed the transition from potential-enemy/befriended-stranger to rejoiced-arrival was the presence of the brass plates:
"…there was great rejoicing among the people of Zarahemla; and also Zarahemla did rejoice exceedingly, because the Lord had sent the people of Mosiah with the plates of brass which contained the record of the Jews."
Note that the rejoicing is because of the brass plates. The plates will have this effect for two reasons. The first is the very possession of the plates would mark Mosiah as an important man, for we must suppose that such records would have been rare on most writing materials, but quite rare on metal plates. Thus the very plates themselves would serve a talismanic function identifying Mosiah as an important man. Since the acceptance based on genealogy occurs after the initial reception, it appears that it was the very fact of the possession of such an important item as the plates was the initial pivot on which swung the acceptance of the Nephite refugees.
Much later, the examination of the content of the plates would show the common genealogy of the Zarahemlaites and the Nephites. This common genealogy would provide a linkage of responsibility between the two peoples, and make their combination into one people less of a stretch than one might imagine. It would be seen as long lost relatives rejoining.
Biographical, Mosiah: We have already suggested that Mosiah was not the king. Nevertheless, he must have been of Nephi's lineage both because he is later made king, and because he had access to the brass plates. Those plates would have been kept with the kingly line (Jacob and his descendants never mention transmitting the brass plates, only the set we know as the small plates of Nephi). Thus Mosiah had to have the genealogical right to have access to where they were. As we shall see later, Mosiah took more than the brass plates, he also took with him the Liahona and the Sword of Laban.
The Book of Mormon is entirely silent about the people who remained in Nephi, and indeed, who it was that constituted the threat to Mosiah and the believers in God. We may expect either a new conquering invasion of Lamanites, or the leaders of the Nephites turning on the people of God as those leaders became more and more wicked. Either possibility is plausible, and the result of either would be that the City of Nephi becomes a Lamanite holding (using the definition of Lamanite as those unfriendly to the Nephites).
Biographical, Zarahemla: At this point we have only the barest of information about Zarahemla, but it is curious. We know that Zarahemla is the leader of the land, and that the land is named after him. Of course it is not unusual to name a city after its founder, but placing Zarahemla as the founder of the town is problematic. Amaleki indicates that the people of Zarahemla have been in this land since their arrival:
"Omni 1:16 And they journeyed in the wilderness, and were brought by the hand of the Lord across the great waters, into the land where Mosiah discovered them; and they had dwelt there from that time forth."
Sorenson suggests that being in "the land" is covering a larger territory, and not referencing Zarahemla specifically:
"The people of Zarahemla" seem to have been named after their leader, who reported to Mosiah that his ancestors had arrived from the Mediterranean area by boat and that he was a descendant of "Mulek," a son of Zedekiah, the last of the Jewish kings before the Exile. The voyage arrived first in the land northward, then moved south. Probably they first settled at the east-coast site known later as "the city of Mulek" (note Alma 8:7). "And they came from there up into the south wilderness" (Alma 22:31), where Mosiah later encountered them. Factions had warred among themselves; Zarahemla was now chief over one group (Omni 1:17). If the city of Zarahemla was named after him (or his father), then his group would not have been in that spot for very long, although they might have lived in the general locale for some time. (Sorenson, 1985. P. 148).
This makes geographical sense, as they only way the Mulekites could have been in the area where they arrived would be to stay along a coast, and clearly Zarahemla is not a coastal town. Therefore they did move in the greater geographical designation of "the land" which in this case would have the same meaning as the promise Lehi gives for "the land" which was not limited to the specific location where Lehi lived in the New World, but extended to the whole of that area.