Which of the following settlements was located far to the north.

A) Port Townsend

B) Seattle

C) Walla Walla

D) Centrailia

Assuming the settlements are located in the same place where they are today, I would say the correct answer is A. Port Townsend.

I've looked at the map of USA, particularly the Washington state area, and Port Townsend was the northernmost location in that state - Seattle, Walla Walla, and Centrailia were located further down to the south.