Where does “Napa” come from?

Napa (English) comes from Japanese 菜っ葉, from Japanese 葉, from Middle Chinese 葉.

Ancestry of “Napa”, step by step

Step	Language	Word	Meaning
1	Japanese	菜っ葉	leaves of any vegetable
2	Japanese	葉	leaf, needle, blade; a season, an age: a shorter...
3	Middle Chinese	葉	—

Napa — Etymology, Origin & Word History | Etymology Explorer