This is related, but if you're looking for city names, the main place endings are "stadt" (town), "t(h)al" (valley), feld (field), dorf (village), berg (hill), burg (fort), heim (home), au (meadow), hof (farm), ort (place), and wald (forest). These were used by German colonists in Eastern Europe (and to a lesser extent, Africa) in the naming of their settlements. The first element is often something like glück (luck, happiness), frau (woman), reich (rich), neu (new), alt (old), fried (peace), freud (joy), various colors (i.e. rosen - red), names of rulers, and of course first names and surnames. Like all European settlers, Germans also named many places from towns and cities in Germany or elsewhere in the German-speaking world, with or without "Neu-" before them.
Problem is the majority of Montana isn't particularly mountainous compared to Wyoming or Colorado where the Continental Divide cuts right through there. Although a more sane division of the US West (like what Russia/Soviets did in Siberia or basically just avoid lines of longitude as much as possible) would probably assign Western Colorado to Utah or make it its own state.
I will say it's one of my AH pet peeves that people tend to avoid using indigenous toponymy and resort to much less creative toponymy (basic words in whatever language or "new X") when historically the languages of indigenous people lent us a huge amount of place names throughout the places colonised by Europeans.
Mexico with German-level literacy, even if you keep the population the same, would be almost game breaking in Vicky 2.