For decades I've wondered where my grandfather Ephraim Rees Davis got his name.

Davis, of course, came from his father's family.

Rees was his mother's father's name.

And today, by pure serendipity I web-searched the name of his birthplace, Samaria, ID, with no other text, and...

"The Samaritans are an ethnoreligious group originating from the Israelites of the Ancient Near East. Ancestrally, Samaritans claim descent from the tribe of Ephraim and tribe of Manasseh as well as from the Levites, who have links to ancient Samaria from the period of their entry into Canaan, while some Orthodox Jews suggest that it was from the beginning of the Babylonian captivity up to the Samaritan polity under the rule of Baba Rabba. (Wikipedia)"

"My" Ephraim was the last born to his mother, and because they were a religious family from Samaria, there's the answer!

Seek well, and all things will be revealed unto you.