Donna,
The granites are a locality/color phase of S. ater.
S. Varius is the San Esteban island chuck, or piebald chuck.
S. Hispidus is the Angel island or spiny chuck.
Calico chucks are varius X hispidus hybrids. Since both varius and hispidus get big, your little hybrid should as well. It will likely exceed 20 inches in lenght, eventually. Varius can get slightly larger than hispidus, and I think the maximum length is somewhere around 27 inches.
I hope this helps clear things up.
Nick

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