A typical rock pocket mouse is about 170 millimeters long from its nose to the end of its tail, shorter than an average pencil. And at just 15 grams, this tiny mouse weighs about as much as a handful of paper clips. You can find populations of rock pocket mice all over the Sonoran Desert in the southwestern United States.
There are two common varieties—a light-colored variety and a dark-colored variety. There are also two major colors of substrate, or surface materials that make up the desert floor. Most of the landscape consists of light-colored sand and rock, but patches of dark volcanic rocks that formed from cooling lava flows are found, separated by several kilometers of light-colored substrate.
