Six amphibian and six reptile species inhabit Lassen Volcanic National Park. They are often considered together because both are poikilotherms, animals that lack the ability to generate their own body heat, relying instead on their environment to regulate body temperature. Amphibians spend the early part their life cycle in water as larva before metamorphosing into adults that live on land. Toads are a good example. As tadpoles, they are restricted to aquatic environments, but spend almost all of their time on land as adults. In contrast, reptiles are generally terrestrial throughout their life cycle. Amphibians are also characterized by moist, highly vascularized skin while reptiles are typically covered by scales.

In marked contrast to the amphibian’s preference for moist, damp habitats, reptiles prefer dry, rocky places. Lassen’s reptile fauna can be divided into two groups - lizards, and snakes. The three lizard and four snake species are seen at varying degrees of frequency.

The sagebrush lizard can be seen in drier habitats climbing on rocks and heard skittering through dry leaves. The Northern and Southern alligator lizards are usually difficult to see due to their nature of hiding under rocks and logs.

The four snake species that are known to occur in the park are the rubber boa, Western terrestrial garter snake, common garter snake, and the striped whipsnake. Very little is known about the reptiles in Lassen Volcanic National Park and more research is needed to learn more about the habits and number of reptile species that occur in the park.