Tip - Use Google Analytics to Identify the pages

Go to Google Analytics and compare all of your site pages with the past dates to see on which pages your site lost traffic first. Due to panda penalty although overall pages of your site will lose rankings and traffic but the ones which were hit first are probably those which were the main cause, so try exploring all of them to figure out the issue. 

This doesn't mean you should ignore the rest of the pages, panda peanlty = complete site content quality audit.