Well, the dialects are very much distinct, since the valleys were very poor until the 1950ies and so there was not much cultural exchange. When I went to middle school (age 10) in the neighbour village, I could not understand all words, even though those villages are only about 1000-2000 inhabitants big.
Different valleys are even more distinct, although they mostly do understand each other. Ötztal dialect for example is so distinct from the others that it is a UNESCO world culture heritage.
Wow that's actually pretty amazing. I also find it interesting, that the USA has a large amount of very different accents, while australia is the same size, and yet hasn't got many different accents.
The interesting part about the USA is, that the southern accent is closest to the original english spoken by the settlers. British english and other dialects evolved from somewhat that origin.
The differences between Australia and USA are also historic. Australia was used to imprison british people, hence the dialect evolved from there, but slowly due to low population.
In the US, the settlers were from all over europe helping the language to evolve in several directions.
Hungary for example, has also little to no dialects at all