That's a nice parallel, Peter, I always though like that, too. These coins are utterly interesting, so much I even went for them although my area of collecting usually starts with 19th century.
It was expensive to transfer copper to other mints in Russia and back to Siberia again so mint opened in Suzun, 150km south of Novosibirsk(The latter didn't even exist in 18th century BTW). For the convenience and reasons Peter mentioned, Siberia used a different monetary system for a while, although of course, rouble was accepted.
Another peculiarity is that KM is not actually a true mint mark. Rather it denotes the copper came from Kolyvan mines - it stands for Колыванская Mедь (Kolyvan copper), which was fully written on the edge of bigger coins in early 1760s (no KM letters on these pieces). Interesting to notice how the copper had to travel from that mining town over 200km south, to Suzun, which was, I presume, possible only in the summertime through Ob river. When Siberian monetary system was abolished and Suzun mint started to mint regular royal copper coins in 1781, they was also marked with KM, which finally changed to CM (Suzun Mint) only in the 1830s.
I also attached a photo of a piece from my collection, the biggest Russian copper coin, a 10 kopek piece, which weights whooping 67 grams.