Having a few spare minutes, I decided to actually visit some of the sites on my page of links. The Easton site had some great links to pages on Italian dialects, among which I found this:
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There are two major groups of Italian dialects, excepting the Sardinian group which is considered another language entirely. These two groups are separated by the Spezia-Rimini line, named for the two cities near which it passes; the line runs east-west across the peninsula, for the most part following the border between Tuscany and Emilia-Romagna, then cutting into the Marches. Above the divide lie the Northern (Settentrionale) dialects; below it the Central-Southern (Centro-Meridionale) dialects.
The Septentrional or Northern dialects in turn are divided into two main groups: the largest of these geographically is the Gallo-Italic group, encompassing the regions of Liguria, Piedmont, Lombardy, and Emilia-Romagna, as well as parts of Trentino-Alto Adige. It is named for the Gauls which once inhabited this part of Italy, and who, it seems, left traces of their Celtic speech in the modern dialects. Next largest is the Venetic group, whose borders loosely follow the region of Veneto. (ea)
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This fits nicely with what I heard, and with what a friend who lives locally told me of his mother's dialect. She comes from a small village near Rimini, and one example of the dialect is the word for "Madonna", which is "Madosca". The error I made was in assuming that Sammarinese was a distinct dialect, when it was always much more likely to be very closely related to the dialect of the region of Italy surrounding it.
