Where does “Yamagawa” come from?

Yamagawa (Portuguese) comes from Japanese 山川, from Japanese 山, from Japanese 陰, from Middle Chinese 陰.

Ancestry of “Yamagawa”, step by step

Step	Language	Word	Meaning
1	Japanese	山川	mountains and rivers; mountain rivers
2	Japanese	山	a mountain or hill; a mine; a heap, pile
3	Japanese	陰	shadow, shade; hidden side; yin
4	Middle Chinese	陰	—