Top US city turned up a source of wool (6)
I believe the answer is:
alpaca
'source of wool' is the definition.
'alpaca' can be an answer for 'wool' (alpaca is a kind of wool). I'm not sure about the 'source of' bit.
'top us city turned up a' is the wordplay.
'top' becomes 'cap' (both can mean to beat or outdo).
'us city' becomes 'LA' (Los Angeles).
'turned up' shows that the letters should be reversed in order.
'cap'+'la'='capla'
'capla' back-to-front is 'alpac'.
'alpac'+'a'='ALPACA'
Can you help me to learn more?
(Other definitions for alpaca that I've seen before include "Llama relation" , "S American animal related to llana" , "Type of llama" , "Llama-like domesticated animal, valued for its wool" , "Llama with long silky hair" .)