Physical structure shortly to be seen moving west across northern state (7)

I believe the answer is:

montana

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'state' is the definition.
(state of the US)

I can't explain the remainder of the clue.

(Other definitions for montana that I've seen before include "American state, capital Helena" , "NW US state" , "State of NW USA" , "North-western state bordering Canada" , "North-west US state bordering Canada" .)

I've seen this clue in The Times.

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