Stangeland Family of South Dakota

I am researching my grandmother (wife of Severt Kloppen) whose maiden name was Aletta Petra Stangeland. She and her family immigrated to South Dakota from Norway around 1900. I am seeking information about her forebears in Norway. I don't know where in Norway they lived, but as far as I know, they always resided in South Dakota in this country. Their children were named Gladys Irene Kloppen, Thelma Kloppen, and Delores Kloppen. Thank you for any assistance you can provide.