Answer: Dermacentor sp. tick, adult male
Wow, lots of great discussion on this case! Thank you readers for providing the identification keys and references. Some of the key features that identify this as a Dermacentor are the ornate scutum, short mouthparts, and festoons. Examination of the spiracular plates is necessary for differentiation between D. variabilis and D. andersoni, and, as Jon mentioned, you can't see the spiracular plates well enough in these photos to make that distinction.
I believe that the CDC pictorial keys that Florida Fan was referring are HERE. These are definitely a good place to start when performing arthropod ID. I'll also put in a shameless plug for a benchtop reference guide that Blaine Mathison and I published with the CAP Press that provides guidance for identification of arthropods to the genus level (which we don't make money on, so I don't feel bad mentioning). Finally, Blaine and I published a review on identification of medically-important arthropods through Clinical Microbiology Reviews that you can access HERE. If you don't have access to the full text, send me an email at email@example.com and I will send you a copy.