Source of chocolate is California, and California’s outskirts mainly (5)
I believe the answer is:
cacao
'source of chocolate' is the definition.
(I've seen this before)
'california and california's outskirts mainly' is the wordplay.
'california' becomes 'ca'.
'and' is a charade indicator (letters next to each other).
'california' becomes 'ca'.
'outskirts mainly' becomes 'o' (I can't explain this - if you can you should give a lot more credence to this answer).
'ca'+'ca'+'o'='CACAO'
'is' is the link.
Can you help me to learn more?
(Other definitions for cacao that I've seen before include "Plant" , "Tree yielding chocolate" , "Tree for cocoa bean" , "Tree from which chocolate is made" , "Tropical tree, the source of chocolate" .)