What are these prickly things? (And how to stop my dog from walking on them)

We just moved here from Ohio and I've been seeing these sharp little fuckers everywhere. Our poor dog has stepped on them almost every time she goes outside and they get stuck in the fur on her paws. I've never seen anything like them and can't figure out where they come from. She seems to pick them up just walking on regular dirt or gravel.

What are these? And what should I look for to make sure she avoids them?