Hoary marmots are large rodents that live mainly in alpine areas. Their loud, clear warning calls are a common sound in the mountainous regions of Denali. Marmots are burrowing animals and their lifestyles revolve around their burrows. Marmots live in loosely formed colonies made up of small family units (a pair of adults and their offspring). Colonies usually occur as "neighborhoods" of two or more family-based colonies. Marmots live in areas that provide good subsurface protection, escape from predators, food supplies, and relief from annoying insects. These areas often occur at high elevations near cliffs and rocky outcrops, and at the base of talus slopes.

Hoary marmots are obligate hibernators. In Denali, they are usually active from May through mid-September, and they hibernate the rest of the year. Members of a family usually overwinter in the same burrow or hibernaculum. Mating takes place near the end of hibernation, however marmots usually only breed every other year. A single litter of 2 to 5 pups is born within a month of mating. Young marmots stay with their parents until they reach sexual maturity at 2 to 3 years of age. They disperse away from their natal colony after they reach sexual maturity.

During the short subarctic summer, marmots spend much of their time feeding. Marmots are herbivores (plant-eaters) and they eat massive amounts of vegetation. The stomach and intestinal contents of adult marmots often make up more than 30% of their daily body weight. They feed mainly on herbaceous and annual plants including vetches, sedges, and fescue grasses. Marmots must often travel away from their burrows to find sufficient food supplies. Males mark the boundaries of their territories with secretions from their facial glands, and members of a family group usually forage within distinct territories. During these foraging trips, marmots are vulnerable to predators. When a marmot detects a predator, it often emits several loud warning calls and then runs quickly to a burrow or talus slope to evade the predator. If it does not reach safety, the marmot is likely to end up as a meal for a golden eagle, wolf, or wolverine.