Cattle cross river in Cornwall, following drone over (7)

'cattle' is the definition.
(I know that Beefalo is a beef cattle)

'cross river in cornwall following drone over' is the wordplay.
I cannot really see how this works, but
'river' could be 'fal' (Cornish river) and 'fal' is found within the answer.
'drone' could be 'bee' (I've seen this in another clue) and 'bee' is found in the answer.
'over' could be 'o' (cricket abbreviation) and 'o' is found in the answer.
No letters remain.
This explanation may well be incorrect...

Can you help me to learn more?