These pictures were taken today in Oklahoma City and I am both baffled and curious as to what formation this may be. I was wondering if anyone had any idea?
Well, after a bit of research, I stumbled upon the following image:
This is from a blog of two storm chasers Roger and Elke who I believe witnessed the same cloud formation as you. In the following link:
They refer to the formation as a 'rear flank arc cloud'.
So in conclusion I believe, the formation is a kind of arcus cloud. You can learn more about arcus clouds on wikipedia by following the link:
I hope I have been of help.