[2] Found mainly in rocky outcrops in the deserts of the southwestern United States and Mexico, the rock pocket mouse is medium-sized (length ~18 cm, weight ~12–18g) and nocturnal.

The breeding season spans a few months, starting in February or March, and the litter size is typically between three and six.

Historically, rock pocket mice have been subdivided into as many as ten subspecies (Benson 1933; Dice and Blossom 1937) based on geographical distribution and coat colour.

In the Pinacate mice, they discovered a perfect association between different versions of the Melanocortin-1 receptor (Mc41r6) gene and coat colour.

[3] Subsequent studies demonstrated that there is strong selective pressure maintaining Mc1r allele and coat colour frequencies across the short geographic distances between the light- and dark-coloured rock islands.