Actually its the 17th at Merion that is the Par 3. The 16th is a par 4, the famous rock quarry hole. My guess is that you overshot the fairway off the tee and landed in thick rough. Because of said rough your approach was well short, and you ended up in "No Mans Land," the area highlighted in yellow. I know I've been in the really thick rough that is just outside of No Mans Land before, but I don't ever remember any go a foot and lose a ball shots from No Mans Land.
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edit:Ninja'd by Yankee and Mainz LOL