There is research in Wyoming that shows rattlesnakes will migrate 30-40 miles from summer ranges to winter habitat. I heard about it at a U WYO lecture.

My rattlesnake story. I was watching a logger build a logging road in eastern Oregon in February one year. There was a very rocky section that required blasting large boulders out of the right of way. After one blast, a ball of rattlesnakes larger than a basket-ball was dislodged and started rolling down the hill flinging off snakes in every direction. Fortunately it was very cold and the snakes could hardly move back to any hole in the ground. Still didn’t stop everyone from running away.