About 50 species of mammals are known to live in Montezuma Castle National Monument. Some animals, like desert cottontails, ground squirrels, elk, and mule deer, are common and may be seen by a majority of visitors. However, many desert animals are inactive during the day, so sightings can be truly special events. Tracks and scat are the most common signs of an animal's presence.
Montezuma Castle's hot climate and lack of water seem to favor small mammals. Because of their small size, these animals are less able to migrate, but have an easier time finding shelter and require less food and water to live. Rodents are numerous: there are ten species of mice and rats alone. Beavers, the largest North American rodent, are occasionally seen along Beaver Creek. Larger mammals, like elk, mule deer, and mountain lions, must cover more territory in order to find food and water, and sometime migrate to nearby mountains during the summer. In Arizona, around 80% of a mountain lion's diet consists of mule deer, so these animals are never far apart. However, unlike mule deer and elk, mountain lion sightings are very rare.