Green’s Dictionary of Slang

(US) a sausage, a frankfurter, a hot dog.

1911		L. Pound ‘A Second Word-List From Nebraska’ in DN III:vii 544: groundhog, n. Sausage. ‘Give us that there groundhog.’.
1936		H.W. Bentley ‘Linguistic Concoctions of the Soda Jerker’ in AS XI:1 43: GROUND HOG. Frankfurter sandwich.