We have no later maps showing the Great Gulf. The geography shown here is based on an early sketch map from volume IV of The History of Middle-earth, and is not entirely consonant with the shape of Middle-earth later established in The Hobbit and The Lord of the Rings (neither of which had been written at this point). Indeed, there is no room here for any of the lands in which those later books take place, with the Blue Mountains instead extending all the way to the Straits of the World and the mouth of the Great Gulf.

To match this layout with later developments, we would have to imagine the northwestern lands of Third Age Middle-earth interposed between the Blue Mountains (which lay to the far northwest) and the Great Gulf (which lay to the south of any known lands).