I believe that they were on a spur on the southern Blue Mountains. They were probably an old off shoot from Nogrod that the southern one, right?) It is interesting bevcause the Tale of Years says (ca 40 SA: Dwarves
leave their cities in the blue mts to go to Khazad-dum) Since it is mainly thought that Nogrod and Belegost were destroyed in the splitting of the Ered Luin, perhaps Tolkien wanted to mean that the main cities were destroyed, but parts of them (suburbs, if you will) were just abandoned.
________
Mercedes-Amg