I found Gilbert & Anna in the 1885 Houston Co. Minnesota Census.
1915 Ward Co. North Dakota
Anna M. Rasmussen, 50
Bertha C., 15
I can't find Anna after this Census.
If you decide to pursue your search in Ward County, the following two organizations might be able to help you.
Mouse River Loop Genealogical Society, www.rootsweb.ancestry.com/~ndmrlgs/
Ward County Historical Society, www.wchsnd.org/archives.html