Measure following clean-up operation in American state (10)
I believe the answer is:
Here is my best explanation:
'american state' is the definition.
(Washington is an example)
'measure following clean-up operation' is the wordplay.
'measure' becomes 'ton' (ton is a kind of measure).
'following' means one lot of letters go next to another.
'clean-up operation' becomes 'washing' (washing is a process of cleaning up).
'ton' after 'washing' is 'WASHINGTON'.
'in' acts as a link.