Disaster losing California in fellowship (5)
I believe the answer is:
amity
'fellowship' is the definition.
(I've seen this before)
'disaster losing california' is the wordplay.
'disaster' becomes 'calamity' ('calamity' can be a synonym of 'disaster').
'losing' indicates named letters should be taken away.
'california' becomes 'cal'.
'calamity' with 'cal' taken out is 'AMITY'.
'in' is the link.
(Other definitions for amity that I've seen before include "Accord" , "Friendly feeling, fraternity" , "Friendly relations" , "Cordial friendship" , "Friendliness" .)