Quite a lot of different breeds have that chipmunk-colored chick down, so unfortunately it is probably not going to be possible to identify it for sure (was this, like, a McMurray 'rare exotic free chick' type thing?)
I hate to say it but there are many breeds that look like little chipmunks. EE's, and brown leghorns are 2 types that I have that looked like chipmunk-chicks. I know there are other breeds with similar apperiances as baby chicks. Sorry, I guess that's not much help.
Basically any bird that grows up to have a partridge-looking color, or duckwing, even gold laced, or black breasted red, all have the chipmunk look at a young age. So, that narrows down to ALOT of breeds.
2 Rhode Island Reds, 1 Silver Laced Wyandotte, 2 Silkies, 2 Modern Game Banties, 1 Black Sumatra, 1 Golden Campine, 1 Bearded Buff Laced Polish, and 1 Birchen OEG banty, 1 horse (soon to be 2) 3 cats, 1 dog, and several fish.