If you see grass growing in the entrance of a den, then it's a good clue that the Den is no longer in use by the groundhog. However, other animals like to use old groundhog dens to hide and live inside. Foxes, opossum, skunks and raccoons will use abandoned dens left over from groundhogs.
Baby groundhogs are born with no fur and are blind and helpless and approximately four inches in length. Baby groundhogs open their eyes at about 4 weeks old, they don't leave the den to see the outside until they are around 6 to 8 weeks old.
Groundhogs are solitary animals, except during their breeding season, and by the end of summer, the young groundhog will move away from its mothers den and will establish its own permanent" burrow.