You know spring is in the air when you see rattlesnakes doing this!
The most common species of rattlesnake to "dance" is the Western Diamondback!
I found a great article online explaining this behavior. Apparently seeing rattlesnakes "dance" is a common thing for some folks. Check this link out for more info http://corbinmaxey.com/http://ag.arizona.edu/BTA/whatsnew/snakedance.html