I'm assuming that it fell from above. It was pretty cold so it was probably too lethargic to strike. Either way, It nearly scared the lunch out of me. I was on lead too... would have taken quite the whipper on top of being bitten by a freakin rattlesnake 400 feet off the ground. Lucky for my climbing partner, he had the option to take a slightly different route.
Not buying that the snake "fell from above." It found a route to its stance on the side of the cliff. I encountered a rattlesnake on top of a pinnacle near the summit of Baboquivari in southern Arizona. Only way for humans to reach this summit was via fifth class roped climbing. Snakes go wherever the food goes; rats and mice can climb to amazing places far up the side of cliffs.
I'm actually far more conscientious now about just blindly jamming my hand in a crack. Kinda sucks. haha. I'm familiar with baboquivari. It's a beautiful place. Regardless of the location, climbing is dangerous... in more ways than we know!