Um...not gonna lie, got this one thinking about potential mountain names with six letters, and got it on my second shot. Let me go back and figure out the proper method...
Well I got it on my first wild-assed guess. Even back-solving looks too hard for me. My best hunch is that there are names of mountains immersed in or altered in grid entries. The problem is that there are so many mountains that almost any string of letters is, or is close to, a mountain name.
Yes! The second hint helped. You can move entries into the black areas on the left and right of the puzzle: from the bottom upwards on the left: DOZENS, NODES, DONE -> DEN, and on the right: ALICIA, CILIA, LAIC -> ALI. It was only my lack of familiarity with US mountains that slowed me down!