The sound of a rattlesnake is unmistakable once you’ve heard it once. But this sound wasn’t on my mind when I almost stepped on one a few weekends ago. I was in the Santa Rita mountains of southern Arizona. The highest peak, Mt. Wrightson, looms 7000 feet above the Tucson basin.

In late March, mountaintops like these are in the final clutches of winter. Snow patches and ice survive on north-facing slopes, trees have yet to leaf out, and perennial forbs are just beginning to push through the topsoil. It is a quiet and cold landscape – not the place one would expect to see a snake.

Yet that snake did appear, at 8800′ elevation on a day that couldn’t have been much warmer than 60°F. Despite its kind and persistent rattling I put a footstep just a few inches away from its body before recognizing that sinuous movement and particular shaking sound.

Here it is – the twin-spotted rattlesnake, Crotalus pricei (identification by Dennis Caldwell). This species is protected in Arizona, and was a first sighting for me.

I was curious about why a snake like this would be out on such a cold day so early in the season, and asked a few herpetologists who know more than me about the subject. Two ideas came up.

First, drought might have pushed this snake out of its hibernation. Limited moisture in the environment can mean slow dehydration – so better to chance a cold and prey-poor environment than face a sure death from lack of water. Second, microclimate variation means that a chilly air temperature might translate to a reasonably warm temperature immediately above rocks exposed to the sun in just the right way. This snake might have been taking advantage of warmer conditions immediately near its home. I like imagining all the fine-scale variation in an environment that we humans have difficulty perceiving.

Ultimately I don’t know what caused this snake and me to cross paths. I paused for a quick photograph, then left the snake to its business, whatever it may have been.