Unearthing surprises

I was sincerely shocked that I found this larger than a typical sized specimen in my driveway. It was burrowed deep and only a portion was visible but I was pushing my son in his car when I noticed it. I don’t know how it got there! I’ve lived here for just about 10 years and have skipped right over it. I don’t know how any of these got there in the sense that I actually went to a river bed and found nothing there yet I’m finding these at my house. I did post my previous finds to my amateur geology/rock collecting group and they were quite happy for me to have found these out and about in my yard. Some people said they have found similar things on their property but I don’t know just how typical it is for Texas! 

It does make me wonder a few things such as, did the people putting gravel in our driveway bring them from another place before we moved in? Or are they just there? Since I have found others while digging, I can’t really say for sure.