There are several growing in the woods behind my house. I’m located in the upstate ( Easley ).
this is an insect gall, not a typical growth of the oak; it is called a Wool-sower wasp gall or Strawberry gall, made by the tiny wasp Callirhytis seminator. It is not common, but not rare either.
I apologize for the delay in my reply. I had software issues that only now have been fixed. Thank you for your patience.
Dr. Steven Hill, Botanist, SCNPS