Thorin in the Blue Mountains

[Inziladun]

Originally Posted by The Mouth of Sauron

I seem to remember that in the Appendices mention is made of dwarves living in the Ered Luin in the Fourth Age. It might well be that their permanent settlements there throughout history had hereditary rulers who were not of Durin's house.

I would guess you're referring to this from Appendix A , "Eriador, Arnor, and the Heirs of Isildur":

But Dwarves dwelt, and still dwell, in the east side of the Blue Mountains, especially in those parts south of the Gulf of Lune, where they have mines that are still in use.

The cities of Nogrod and Belegost, certainly, were not of the Longbeards.

However, after the end of the First Age, I don't recall any mention of Dwarves having established settlements there prior to Thorin's colony being established in T.A. 2802 (TOY).

It was said, also in Appendix A, that when the Witch-king overran Arthedain in T.A. 1974, that King Arvedui took shelter "in the old dwarf-mines near the far end of the Mountains". Since his next act was to seek aid from the Snowmen of Forochel, it seems clear those mines were near the northern end of the Mountains, and were not occupied.

The first reference above to mines being in the south of the Mountains, might simply refer to Thorin's settlement. At any rate, I think it unlikely Thorin would have gone to the Ered Luin and founded his own settlement if other Dwarves were already established there.