The following link has a nice shot of a woodchuck looking a lot like a rather stout squirrel. Apparently their color varies and they can appear black in some cases. This link shows the range coming very close to Texas; so, who knows? Maybe they've actually extended their range into Texas. So far, though, they're not included in the list of Texas mammals on the Texas Parks & Wildlife website.
Woodchuck | Marmota monax | Mammal
JohnK