It was Anfin's marriage license to Selma D Brenson. The actual article wasn't posted though so I couldn't verify. What's interesting, is they type Anfin as Arnfin. I also had a hard time verifying where Anfin's sisters were born. It was listed on the 1870 Iowa Census, however the handwriting is hard to read. I think it says Wisconsin, but I'm not positive.
I did just stumble across an 1885 Clear Lake, IA Census that listed their last names as Petterson. Again, I can't see the actual record. SO I can't verify.