Timber Rattlesnake
Crotalus horridus

Size: 4 1/2 - 5 1/2 ft
Eastern 1/3 to 1/2 of the state, usually found in heavily wooded, rocky terrain with dense cover.  One of the most venomous snakes in Oklahoma, this snake has a really quiet nature, and will usually not strike out except for defense. 
A 4-foot wild-caught timber rattlesnake from Willis, OK, as viewed in its natural habitat.