Forged in what sense?
In this case, there is only one Received line; it's the one added by our machine, so it's (hopefully) trustworthy. However, Received headers below that line could potentially be forged.
In that line, the first item (mail.giraffedesign.com) is the HELO string sent during the SMTP transaction. The second (wvdm32.wenatcheevalley.com) is the reverse DNS lookup on the client IP address (the point where the mail hit our system). The third is the most useful piece of information - the client IP (220.127.116.11).