Very interesting!

You see these neat little red islands of "other dialect divisions" - surely areas of detailed study amongst a map that is greatly generalized, probably due to the paucity of in-depth linguistic data.  The neatest little one is right on the Iron Range, and we can thank Dr. Mike Linn, recently retired from UMD and author of 'Origin and Development of the Iron Range Dialect (1988)'.  Mike identified something like 30+ different dialects just in this small geographic area.

I was lucky enough to study cultural linguistics a few semesters with Mike before he retired, and he was absolutely brilliant, his experiences were endless, and you could talk for hours with him, and feel completely comfortable doing it. There was a post earlier in the year detailing his retirement and some accomplishments:
http://www.perfectduluthday.com/2011/04/27/tongues-tied-umd-linguistics-retirement/#comments

And, Matilda, hopefully properly using some knowledge gained from Mike: pin (/pɪn/) and pen (/pɛn/) have separate ɪ & ɛ phonemes..i.e. lit and let are a more distinguishable pair of words with the same phonemes as pin and pen.  don (/dɒn/) and dawn (/dɔn/) also have separate phonemes, ɒ & ɔ, respectively,  an open-mid versus open vowel (see: international phonetic alphabet). What makes up these seemingly indistinguishable differences is how the words are sounded in the human speech anatomy, and you have to factor in your aural perception of sounds and your own dialects that you possess. 

So, thanks again Mike. Your works and passed on knowledge lives on!