Not a black, But darker than some, this is a female Northern Timber Rattler.
In the northland the Timber Rattlesnake, formerly Crotalus h. horridus, now just C. horridus) probably needs no introduction. They are the big (4 to 5 feet long when adult, occasionally a few inches longer) black or yellow (occasionally olive, especially when a juvenile) rattlesnake that is quick to buzz if disturbed and all too often quick to strike if too closely approached. Preferred habitats include sun swept open areas and equally sunny, rocky mountainsides or summits. They, of course den and hibernate, often communally, from late autumn to early spring but wander separately and widely during the summer. A live bearing species (as are all rattlesnakes) a litter may vary from 2 to 8-, 9- to 12-inch long youngsters.

Once ranging in the east from Maine to Virginia and the highlands of Georgia and in the west from se Minnesota to ne Texas, it has been extirpated by humans/habitat destruction from many areas. South of these areas the niche was filled by the southern subspecies, the Canebrake Rattlesnake (now considered by geneticists as merely a color variant).

So call it what you wish. I prefer to recognize each differently—Timber Rattlers in the north both in lowlands and mountains and the beautiful Canebrake in the south.

Comparisons	Timber	Canebrake
Ground Color	Black, olive, or yellow	Tan to pinkish
Markings	Usually no banding on tail when adult No postorbital stripe Weak or missing vertebral stripe	Light banding usually visible on black tail Prominent diagonal postorbital stripe Prominent orangish vertebral stripe