Call 150 out as leaving pass in the mountains (4)

I believe the answer is:

alps

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'pass in the mountains' is the definition.
'alps' can be an answer for 'mountains' (European mountain range). I'm not certain of the 'pass in the' bit.

'call 150 out as' is the wordplay.
'p50' becomes 'CL' (Roman numerals).
'out' suggests deleting specific letters.
'as' becomes 'ps' (I can't explain this - if you can you should believe this answer much more).
'call' with 'cl' removed is 'al'.
'al'+'ps'='ALPS'

'leaving' acts as a link.

Can you help me to learn more?

(Other definitions for alps that I've seen before include "Mountain pastures" , "Pals seen in mountains" , "Mont Blanc mountains" , "Slap (anag.)" , "Pals put on the mountains" .)

I've seen this clue in The Irish Independent.

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