Garry leaves cap in valley (4)

I believe the answer is:

glen

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'valley' is the definition.
(glen is a kind of valley)

I don't understand the rest of the clue.

(Other definitions for glen that I've seen before include "Narrow valley with a stream" , "Narrow, deep mountain valley" , "Highland valley" , "Narrow Scots valley" , "Valley, dale" .)

I've seen this clue in The Telegraph.

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