Crossword Genius

Two US states that share a capital (4)

Ross

I believe the answer is:

riga

'capital' is the definition.
(capital of Latvia)

'two us states that share a' is the wordplay.
I cannot really understand how this works, but
'a' is found in the answer.
The remaining letters 'rig' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

(Other definitions for riga that I've seen before include "trading centre in Latvia" , "Latvian capital" , "A rig in Latvia" , "Baltic port" , "port in Latvia" .)

I've seen this clue in The Guardian.
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