Gilbert (Gulbrand) Amundsen Gran and Family

I am trying to find the parents and family of Gilbert who emigrated (sailed) to the USA (Wisconsin) in 1871. He was born in 1848 and died in Wisconsin in 1937. In 1879 he married Inger Lunde in Wisconsin who is descended from Torkel Snodalen. Although I have a very complete history of the family once they moved to North America, I cannot find any links back in Norway. In one census document Gilbert refers to his parent as Amund and Mari Gran but do not have any record of siblings or other family from his generation or his parents. Any help would be greatly appreciated.