From the Encyclopedia of Arda:
Quote:
The Ered Luin, the mountain chain that formed the eastern border of the lands of Beleriand during the First Age, and in which were the Dwarf-cities of Nogrod and Belegost. After the loss of Beleriand at the end of the First Age, the mountains remained, but they were now in the far west of Middle-earth.
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It was my understanding that the two cities were completely destroyed in the War of Wrath, and the mountains broken into two smaller ranges. Dwarves, according to 'The Tolkien Companion' still had settlements and mines in the eastern foothills of the souther range; the northern one being cold and iced over since the breaking.