Study parts of Sacramento (4)
I believe the answer is:
cram
'study' is the definition.
(I know that cram is a more specific form of study)
'parts of sacramento' is the wordplay.
'parts' says the answer is hidden in the clue (I've seen 'part of' mean this).
'CRAM' is hidden within 'of sacramento'.
(Other definitions for cram that I've seen before include "Stuff (facts for exam)" , "Greedily eat" , "Swot (for exam)" , "Press together" , "Crowd or pack to capacity" .)