[oh_sigh]

That is wrong. Almost all of the energy DC uses comes from its interconnect to the RFC grid. Locally, it does look like 2/3rd of the power DC generates is nat gas, and 1/3rd gas or gas-like, but it doesn't make sense in a grid structure to assume that the energy produced near you is the energy you use.

https://www.eia.gov/state/?sid=DC#tabs-1

[connorcpu]

Given that its neighbors' top two electricity sources seem to be Nat Gas and Nuclear, seems probable that most of the electricity comes from those sources

[oh_sigh]

You should really just take a weighted average of all the things putting energy onto the eastern interconnect grid(including grid-tied home solar installations, but those are probably negligible in the grand scheme of things at this point).

The reality is that anyone in the US, east of the rockies and not in texas will have the same 'mpg equivalent' for their Tesla.