For those who have not completed Xenoblade Chronicles X, this page may contain spoilers regarding the plot. Discretion is advised.
Like all Unexplored Territories, its discovery yields an achievement ("The Hidden Millstone Ridge").
Sometime before the events of the game, an alien mech comes to rest in the hollow of the Millstone Ridge. It is sought after by the Ganglion, but rendered unreachable by the Tainted in the area; Tainted will kill anything alive that comes too close. When news of this reaches BLADE the party is sent out to retrieve the mech, assured that the Tainted will not harm them as they are in artificial Mimeosomes insteaed of flesh-and-blood bodies. They locate the mech and send for helicopters from New Los Angeles to retrieve it, and are preparing to leave when Tatsu appears to offer them lunch.
Although well-meaning, this visit immediately draws the attention of the surrounding Tainted: the party is attacked first by three Caro and then by a Sphinx. Once these are defeated three more Sphinxes appear, but are killed by an attack out of the blue from a Telethia. The Telethia eyes the party briefly before flying off, and then the party exits the area.