A study mounted involving Virginia, a US state (6)
I believe the answer is:
nevada
'a us state' is the definition.
(I've seen this before)
'a study mounted involving virginia' is the wordplay.
'study' becomes 'den' (I've seen this before).
'mounted' says the letters should be written backwards.
'involving' is an insertion indicator.
'virginia' becomes 'va' (US state abbreviation).
'a'+'den'='aden'
'aden' back-to-front is 'neda'.
'neda' enclosing 'va' is 'NEVADA'.
(Other definitions for nevada that I've seen before include "Sagebrush State" , "Southwestern US state" , "US desert state" , "Curiously, Dan and Eva are in the US" , "South-west US state" .)