Everyday occasion, ultimately, at Russian river (7)
I believe the answer is:
natural
'everyday' is the definition.
(I've seen this before)
'occasion ultimately at russian river' is the wordplay.
'ultimately' says to take the final letters.
'russian river' becomes 'ural' (I've seen this in other clues).
The last letter of 'occasion' is 'n'.
'n'+'at'+'ural'='NATURAL'
(Other definitions for natural that I've seen before include "person regarded as certain to qualify" , "Genuine, unaffected" , "Accidental" , "Normal - innate - instinctive" , "Simpleton" .)