Settlers claimed ownership of land in the Pacific Northwest primarily through the process of homesteading, which included farming the land for a certain period (typically four years) and clearing the land. The building of structures also established a claim. However, making treaties with local Native Americans was not typically a method of claiming land by settlers, as many did not view or respect the existing land rights of Indigenous peoples.
Thus, the most accurate responses from the options provided would be: "They farmed the land for four years" and "The building of structures established a claim."