[JeffF.]

According to Unfinished Tales It was the hill of Himring that survived as the island Himling off the coast of Northern Ered Luin and not the Gulf of Luhn. It is interesting that this hill, not a mountain, but the highest hill in an area of hills survived as an island but the mountains near it were sunk implying that this hill was raised while the mountains were lowered.

The island of Himling is shown in the map of Unfinished Tales but not in the LotR.