Noun and の adjective
さんがく
この山岳地帯では、少なくともあと三ヶ月は冬の季節が続くだろうね。
Winter will continue for at least three more months in this mountain district.
The mountain peaks are just the mountains. Just because you can only see the peaks doesn't mean the rest of the mountain doesn't exist.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.