I was looking up in the trees for hummingbirds as we walked along the trail. My spouse was about five feet ahead. He suddenly veered away from the trail's edge. A beautiful Diamondback was curled up in the sun. He stared at us; we stared back. He turned away; we continued walking. It was then that my wits returned and I remembered the little emergency camera in my shoulder bag (yep - this was a walk day, not a photography day). I pulled it out of its case and turned back, but by then the snake had lost all interest in us and was beating a retreat.
The Western Diamondback (Crotalus atrox) is the second largest snake in the United States, second only to the Eastern Diamondback. It inhabits dry, rocky, shrub-covered terrain where it can conceal itself inside crevices in the rocks or in mouse holes. These rattlesnakes are generally heavy-bodied, with a slender neck and broad triangular head. Only rattlesnakes have rattles, which are a series of loosely interlocking horny segments at the end of the tail. Each link of the rattle is the remnant of a molted skin; as the snake molts, the last scale loosens but does not fall off. As the snake ages, new rattles are formed with each molt, while old rattles simultaneously fall off. Thus the number of rattles does not indicate the age of the snake.
From the University of Michigan Animal Diversity Web site:
Western Diamondback Rattlesnakes are aggressive and easily excitable. This species causes more fatalities than any other snake in the United States. They are not necessarily apt to attack offensively, but are rather highly defensive. Their rattles are used as a warning sign.(Thanks to Girl Gone Gardening for her comment on rattlesnake aggression. I've edited my post accordingly.)