Mountains of maps? (5)
I believe the answer is:
atlas
I believe this is a double definition.
'mountains' is the first definition.
(I've seen this before)
'maps?' is the second definition.
(printed collection of maps)
'of' is the link.
(Other definitions for atlas that I've seen before include "In Greek myth, a Titan made to support the heavens" , "One of the Titans" , "book of world records?" , "Chart book" , "Asian satin" .)