zsh alias being overridden somehow

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http://unix.stackexchange.com – I'm on a system running OS X 10.8.5. I recently tried to alias ls to ls -G -la command. I opened up ~/.zshrc, put in the alias, relaunched the terminal, but the change didn't take effect. Upon performing which ls, I found out that it's already being aliased to ls -G. This isn't behaviour I ever set up. Is there any way to find out where this alias is being set? (HowTos)