Massinglokken - Lerbakken

I'm hoping someone can help me trace a name change for my G-Grandmother (GGM) and her family. My GGM was born 18 March 1865 near Vinstra. Her name was Ane Amundsdatter Massinglokken and her parents were Amund Mortensen and Karen Andreasdatter and lived on the farm of Massing. I found them in the 1865 census for Nordre Fron. The next record I found for them was on a passenger list for them when they emigrated in July, 1869. The passenger list has them listed as Amund Mortensen (and family). The first record I have of them in the US is the 1870 census for the state of Wisconsin. In that census, they have the name of Amund Lerbakken, which is the name they also used when they settled finally in Minnesota. Sometime between when they were living on the Massing farm near Vinstra and when they lived in Wisconsin, they adopted the name of "Lerbakken". I assume that they must have lived for a short time at some place called "Lerbakken" or "Leirbakken". There are several place names in Norway for called Leirbakken, is there any way I could find out if they lived in one of those places before emigrating? I've always wondered where they adopted that last name and am hoping someone can give me some pointers to help track that down. Thanks in advance,