I don't know the answer, but every quarter from 2010 (America the Beautiful) up that I have received in change are weak like your 2011.
The National Park quarters have a classic Washington obv., they switched back from the "Spaghetti hair" bust of Washington. This is the original model's approx. details.
Yeah thanks. i had noticed the "weaker" looking strike but had never looked into it. Makes perfect sense.