With habitats ranging from thick foothill chaparral to expanses of alpine rock, the Sierra Nevada supports over 250 species of vertebrates, which include fish, amphibians, reptiles, birds, and mammals. This high diversity of species is also the result of habitats in the Sierra Nevada that are largely intact, compared to areas outside the backcountry where various human activities have resulted in habitat degradation or destruction.

Yosemite National Park, typical of much of the Sierra Nevada, is home to 90 species of mammals, including marsupials, insectivores, bats, lagomorphs, rodents, carnivores and hooved animals.

The Virginia opossum is the lone marsupial. Seven species of shrews and one mole comprise insectivores. Lagomorphs include one rabbit, the pika, and three hares. Bats and carnivores number 17 and 19 species, respectively.

Rodents form the largest group with 39 species. The two hooved mammals inhabiting the area are the California mule deer and the Sierra Nevada bighorn sheep.

Mice, chipmunks, squirrels, and gophers are common. Mice and their allies (8 species), chipmunks (8 species), and squirrels (6 species) constitute more than half of the rodent species in Yosemite National Park. Others include marmots, aplodontia, and porcupines.

Carnivores are perhaps the most widely recognized group of mammals in the Sierra Nevada. Its members include the American black bear, bobcat, mountain lion, raccoon, coyote, foxes, weasels, and skunks. Lesser known species like the American marten, fisher, and ringtail are also present. Although grizzly bears once roamed the area, they were extirpated from Yosemite when the last individual was shot in the early 1920's.

Although often overlooked because of their nocturnal habits, bats represent a large proportion of the mammalian fauna. The mobility of these remarkable flying mammals enables them to occupy a wide range of habitats. They are found from the lowest elevations in the Sierra Nevada to over 10,000 feet. They roost in rock crevices and caves, under loose bark and bridges, in attics and tree cavities. North America’s largest bat species, the western mastiff, is a Yosemite resident, as is the spotted bat with its huge ears and vivid white spots. These are the only two species in Yosemite whose echolocation calls are audible to the human ear.

Many of the mammals, like mule deer and gray squirrels, are fairly common and can be readily seen every day in Yosemite. Others, like the wolverine and Sierra Nevada red fox, are extremely rare and might be sighted only once a decade. Of the 90 mammal species on the park’s fauna list, 17 are considered "special status" by either the federal or California state government due to declining population numbers or a lack of information about their distribution and abundance. Currently, Sierra Nevada bighorn sheep are the only park mammal on the U.S. Fish and Wildlife Service Endangered Species list.

Always enjoy wildlife from a distance.
If you disturb the animal, you might cause it to injure itself while fleeing, abandon its young, or display aggressive behavior toward you.

Never approach a sick or injured animal.
There are diseases, such as rabies, which can be passed from animal to human.

Don't pick up or disturb what appear to be orphaned young.
Wild animals rarely abandon their young. Most likely, the mother is nearby, waiting for you to leave.

Don't feed the animals.
This can lead to aggressive behavior and injury to you or others, in which case the animal will usually be destroyed. Also, an animal which comes to rely on humans for its food may not be able to fend for themselves in the wild.