Fangorn and Isengard on the map

[Heidiiii]

In the story Fangorn seems to be right next to Isengard. The orcs burn the forest and the ents emerge to see the forest remains at the foot of Isengard. I haven’t read the book in awhile, but especially in the movies Fangorn is directly beside Isengard. Yet on most all of the maps there appears to be mountains in between the two. Any thoughts or explanations?
Thanks