I'm not an expert on squirrels, but that could be a ground squirrel[1] of some sort. Some varieties of ground squirrel look a lot like chipmunks.
http://naturemappingfoundation.org/natmap/facts/chipmunk_vs_...
http://www.differencebetween.info/difference-between-squirre...
Sadly, that was my most upvoted comment in ~9.5 years on this site.