In Oregon the breeding season begins in early winter; males with enlarged testes have been found in November. By February the testes have begun to decrease in size and by mid March males are no longer in breeding condition. Pregnant females have been observed as early as mid March and no later than mid April. Female Townsend's Moles appear to have only one litter per year. Reproductive data for the British Columbian population consists of anecdotal information for a few museum specimens: a male with enlarged testes was taken on 24 March, and a female with a foetus about 20 per cent developed was captured on 27 April. These data suggest that the breeding season in British Columbia may be later than in Oregon. The gestation period has not been determined for this species, but it is assumed to be four to six weeks.

Females bear one to four young, with three most common. Newborn moles are naked, and lack teeth and distinguishable eyes; they weigh about 5 grams. By 10 days, their skin colour has changed to grey; the fur begins to grow within three weeks of birth. They are completely furred by 30 days, and weigh 60 to 80 grams. Within a month of weaning, young begin to leave their mother's nest and disperse. In Oregon, they disperse in May and June. Townsend's Moles are capable of breeding in their first winter after birth.

The diet of Townsend's Mole is predominately earthworms. In Oregon several studies based on stomach contents revealed that 70 to 90 per cent of the prey is earthworms. Small amounts of other invertebrates (centipedes, millipedes, snails, slugs, insects) and a few small mammals (shrews or mice) have also been identified in stomach remains. Vegetation (bulbs, roots, grass, carrots, parsnips, oats, beans) is also a major food. Probably because of its more restricted habitat, the diet of Townsend's Mole appears to be less diverse than that of the Coast Mole.

A proficient digger, Townsend's Mole constructs several types of tunnels. It makes shallow surface tunnels (5 to 15 centimetres below ground) for foraging and possibly for locating mates in the breeding season. Usually these surface tunnels are used only once. Molehills are deposited on the surface along these runways. Townsend's Mole also makes permanent deep tunnels, usually 10 to 20 centimetres below the surface, although it may construct deeper tunnels (1 to 3 metres deep) under roads, buildings and fencerows. Soil from excavation is deposited as conical mounds above these runway systems. The average molehill is about 43 centimetres in diameter and 17 centimetres high.

In the breeding season, females construct nursery nests in underground cavities where they give birth to and raise their young. The nest chambers are situated 15 to 20 centimetres below ground; they are about 23 centimetres long and 15 centimetres high. Dirt from excavating these chambers is usually deposited on the surface in a large mound 70 to 130 centimetres in diameter and 30 to 45 centimetres high. Each nest chamber has three to eleven lateral tunnels and an escape tunnel that runs from the bottom of the nest to another tunnel or burrow. The nest has an outer layer constructed from coarse grass, moss or leaves, and an inner layer made from fine dry grass. Green plant material is often used for the outer layer and its drying may heat the inner nest. Some nursery nests are used only one year, others may be reused for several breeding seasons. Until a female gives birth, she will readily abandon her nest if disturbed and build a new nest within four or five days.

Captures of marked Townsend's Moles suggest that subterranean movements of adults with established burrow systems are limited: distances between capture sites ranged from 3 to 116 metres and the average distance between captures was about 40 metres. Long distance movements (beyond 100 metres) are usually undertaken in the dry months of summer in poor habitats where earthworms are scarce. When dispersing from the nursery nest in late spring and summer, however, young Townsend's Moles move considerable distances (up to 800 metres) above ground.

This species possesses a strong homing ability. Individuals displaced short distances (100 to 200 metres) by annual floods usually reoccupy their original tunnel systems quickly after flooding. Moles displaced artificially have successfully returned to their originallocations from distances of up to 450 metres. Although Townsend's Moles are strong swimmers, canals and rivers can be major barriers to their movement.

No density estimates are available for the British Columbia population. In Oregon, population densities may reach 12 per hectare in ideal habitats; as many as 805 mounds per hectare have been counted. Densities may be as low as 0.4 per hectare in areas with few earthworms or unsuitable soil.

Dogs and cats are opportunistic predators of Townsend's Moles, but the major predators are owls, particularly the Barn Owl. Most predation occurs in summer when the young of the year are dispersing above ground at night. The young will cross roads when dispersing, and a few have been found dead on highways in summer. In the dairy farming regions of Oregon, young moles are killed by cattle trampling the nursery nests. In lowland areas, winter flooding also takes its toll. Richard Giger counted 62 Townsend's Moles that had died in a severe January flood in his study area in Oregon. Moles may be trapped in their tunnels or die from exhaustion when attempting to swim to higher ground.