Mystery solved. I received this email from a fellow, and much more knowledgeable, Arizonan from the Tucson Herpetological Society.
http://www.arts.arizona.edu/herp/qanda.html
Hi J,
The beast in your photo is an Arizona Black Rattlesnake. It's a subspecies of the Prairie Rattler. They tend to be found in hills or mountains rather than in the lowlands. Young ones are lighter in color with dark markings on the back, and the snakes get darker as they get older. In some populations of them the old adults are sooty black with a scattering of yellow scales. They're not as bad tempered as diamondbacks (my own personal opinion) but their venom is respectable. You probably would not want to get bit. The Latin name for them is Crotalus viridis cerberus - "cerberus" coming from the name of the two-headed black dog that guards the gates of Hades in ancient mythology. Obviously named by someone who considered the snake to be a little intimidating.
On a different topic - thanks for your message, especially with the website reference. I too am an avid shooter with a makeshift pistol range on my property outside of Tucson. We've got two species of rattlers that show up there regularly - diamondbacks and tiger rattlers. My wife and I are both comfortable around rattlers, so we leave them where they are. Pretty much if you don't bother them, they won't bother you, and they just might do you some good.
Again, thanks for the website reference. Now that I know it's there, I'll periodically check it out.
Bill