I don't think it is a Black Snake, not even sure it is a Copperhead. Did you see its head before it went down the hole? If so, was there any white on the lips? It could even be a Brown Snake, but not much to go on here.
John An observer experienced with both Red-bellied and Copperhead snakes with us saw the whole snake clearly before it went down the hole and identified it as a Copperhead. We were at an altitude of a bit over 800m if that helps.