Culture: The rebel Lamanites had sufficient inter-group communication that they could arrange to flee together. This clue tells us that the rebellion was sufficiently well organized and in sufficient geographic proximity to allow uniform action, thus reinforcing the hypothesis that either a single city or one or more kin groups was involved. I read the two facts that they went to a particular location and appointed a king (v. 6) as suggesting kin groups.
Geography: The hill Onidah is called “the place of arms.” It is not the hill Onidah in Antionum from which Alma preached to the farmers excluded from Zoramite worship (Alma 32:4). That hill in Nephite territory is not designated as a “place of arms,” but John L. Sorenson suggests:
In the classic pattern of the ambitious Nephite dissenter, this man went up to Nephi to egg on the king over the Lamanites to war against the Nephites (Alma 47:1). Many of the Lamanite folk, however, did not relish undertaking one more of the seemingly endless series of disastrous wars in which the Nephites always seemed to come out ahead. This time the majority of rebellious Lamanites from the vicinity of the city of Nephi simply fled to a nearby location called Onidah, “the place of arms.” Nearby was a Mount Antipas on top of which they assembled after arming themselves. Onidah clearly was in broken country no great distance from the capital city of Lehi-Nephi. In Mesoamerica, what constitutes a “place of arms” is obvious; it can hardly be anything other than an obsidian outcrop. This volcanic glass was the most convenient, most effective, and cheapest substance for manufacturing arms or any cutting tools (note that Alma 49:2 informs us that “arrows and stones” were the chief weapons of the Lamanites). Trade in obsidian was the mainstay of commerce from earliest times. Some routes over which it moved extended as much as 700 miles.
It happens that one of the most extensive sources of this key material is the hilly zone called El Chayal, approximately sixteen miles northeast of Kaminaljuyú. Spots within the kilometers-wide obsidian exposures at El Chayal are virtually paved with waste chips, where cutting implements have been shaped by chipping. Obsidian from El Chayal was exported widely as early as Jaredite times. So the unhappy Lamanite folk, expecting to have to fight the king’s forces to keep from being pressed into military service, first went to Onidah, perhaps El Chayal, to arm themselves, then moved to the tactical safety of a mountain top.