Hollow areas in the Appalachian Trail (5)

I believe the answer is:

antra

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'hollow areas' is the definition.
The definition suggests a plural noun which matches the answer.

'in the appalachian trail' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ANTRA' is hidden in the letters of 'appalachian trail'.

Can you help me to learn more?

(Other definitions for antra that I've seen before include "Cavities - a rant (anag)" , "Cave!" , "Natural cavities in bone; ratan (anag.)" , "Hollow spaces" , "Chambers" .)

I've seen this clue in The Guardian.

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