This word appears to have been derived by folk etymology from earlier woodshock, q.v., itself a folk etymology meaningfisher, q.v., from an Algonkian word of similar meaning, as Cree o(t)chāk, which also came into English aswejack, q.v. At some time in the eighteenth century the termwoodshockappears to have been transferred from the fisher to the groundhog, in which sense the alterationwoodchuckhas become generalized.
1820  (1838)  One of the men brought in an animal . . . called a wood-chuck, or ground-hog, about the size of a Chinese pig half grown and resembling a guinea pig in shape and species.
1958  While digging, he came upon an animal's burrow, and following it to the end, we found a groundhog, or woodchuck.