northern mountains; mountains to the north
Refers to mountains located in the north, often used in geographical descriptions or place names.
北山にはまだ雪が残っている。
There is still snow on the northern mountains.
この町
The mountains to the north of this town are famous for their autumn leaves.
西山 means 'western mountains', completing the set of directional mountain terms.
北山 refers to mountains in the north while 南山 refers to mountains in the south, the direct directional opposite.
Compound of 北 (north) and 山 (mountain). The reading きたやま is a straightforward kun'yomi combination.