carbon emissions by (US) state: why so different?

What is it about ND and SD that would make them so different on this map of per capita carbon emissions? Or is the map misleading?

http://innovation.cqpolitics.com/multimedia/earth_day_carbon?tab=2

ND has large coal-fired power plants and very few people. See this map of coal deposit: http://www.mapsofworld.com/business/industries/coal-energy/usa-coal-deposits.html

These things are very sensitive to population density and other factors. Case in point is the county where I live. There was about 20 or so years ago a big initiative to force carpooling here in an attempt to reduce per-capita emissions, which are very very high. Somebody figured out, though, that if you took away 100% of the vehicles of county residents, you’d only eliminate 15% of the emissions, because 85% came from traffic on the big interstate that passes through this otherwise sparse area. The great majority of driving here is done by people who start and finish their trip outside the county and do not live, work, or even stop here.