I haven't seen or heard from mom since baby was 4 months. No paternity is in place. She ran off and then after 10 years I get a Nevada order to pay back support? I am confused

A court order?

If so, service was allegedly made, somehow. If nothing else, service by publication.

Find out how. Check with the clerk of court and ask if they will send you a copy of the file.

Obviously, you are going to need Nevada counsel.

No I have no order for anything on the child. Nothing I never knew where she has even lived I have seen the baby once ten years ago. Then she ran off with her and never made contact till ten years later ! I get a certified letter from the state of Nevada saying the mom applied for state assistance and I owe arrearages in the amount of 30,000! I don't even nor ever have been in court for anything with the mom in a decade. Not even for paternity which of course I want.

...I don't even nor ever have been in court for anything with the mom in a decade. ...

This is what's called a "negative pregnant" (pun intended). It means that you are implying you were in court with her more than 10 years ago. What was that all about?

You should respond to the letter, stating that you don't know if you are the father, and if they seek to recover state aid paid to her (which they can do, if they can prove paternity), they will have to prove it (paternity testing).

I don't know if they can seek retroactive child support. Apparently Tennessee allows it, but I don't think all states do.