Ok, here's what is stupid about this.
1. When I renewed my Driver's License just last year, I provided proof of citizenship. Clearly the DPS has access to this information.
2. They are willing to accept COPIES of the proof (copy of U.S. Passport, copy of Birth Certificate, etc.) I could whip something up in about 10 minutes on the computer that would be far more official looking than the real thing.
3. This is not a state law. They're enforcing a Federal law dealing with eligibility to purchase a handgun.
4. They're the GOVERNMENT. Even if they didn't have my DL information proving I'm a citizen, they could find this information out easily.
5. This is a RENEWAL. I've been using my CHL in lieu of a background check to purchase firearms for many years. Didn't they think to check to see if I was eligible to purchase firearms before they issued my initial CHL? How about when they issued me my past renewals?

I've got an official copy of my birth certificate that I'll send them tomorrow. It's not a problem, just silliness.