from mountain to mountain; along the mountains
Describes movement or a route that goes along or across a series of mountains, often used with verbs like 行く or 伝う.
彼らは山伝いに次の村へ向かった。
They headed to the next village, going from mountain to mountain.
山伝いの道は険しいが景色がいい。
The mountain path is steep, but the scenery is beautiful.
Compound of 山 (yama, 'mountain') + 伝い (tsutai, the continuative form of 伝う, 'to go along'). The reading づたい is a rendaku form of つたい.