The largest and stockiest of local squirrels is the yellow-bellied marmot. They can vary in length between 19 and 26 inches and can be identified by the dark head with a yellowish band across the bridge of the nose. Marmots can be found on the rocky subalpine slopes which are close to sources of grassy or herbaceous vegetation where they excavate networks of burrows to protect them from the freezing temperatures. They live in harem colonies and like to bask in the sun of the warm summer days. Sometimes they are known as woodchucks or groundhogs.

Their daily routine can be observed as they are up with the sun and busily foraging along well-worn paths. By midmorning they can be found basking in the sun. After noon, they retreat to their burrows appearing again late in the afternoon basking again atop boulders.  Then a final round of foraging late in the afternoon occurs before they retire to their burrows for night. Various whistles have been identified which appear to alert others in the colony or to maintain spacing between colonies. Marmots are hibernators entering their burrows in September or early October, emerging in spring in April or May.

Breeding occurs in spring soon after hibernation ends. Gestation is four to five weeks with litters of three to eight young. As yearlings, both males and females disperse from their birth colony. During this time they are especially susceptible to predation.