In 1960 this item was purchased in Minneapolis. We thought it was by Phillip Morton who taught at th U of M. I was just looking at it again and the mark is not Morton (which is CM over "Sterling") but two mountain peaks? a stylized M?
See the item and the mark here:
http://www.flickr.com/photos/bldodge/3032642226/
http://www.flickr.com/photos/bldodge/3031802613/
.