Mating occurs underwater during much of the April to October activity period. Permanent water is critical because the aquatic larvae require 2 to 3 years to transform. This species is restricted to perennial streams of low temperature in steep-walled valleys with dense vegetation. Intermittent streams are unsuitable. Primarily nocturnal but occasionally abroad during the day.
Adults are especially active, even moving away from the stream, during or just after rains at night.
Periods of winter inactivity seen in some populations are spent in refuges within or close to the normal area of activity. During drier periods frogs are usually restricted to the stream bed itself. Unlike most frogs, Ascaphus are not known to be vocal. Males may call while underwater but there is no evidence at present. Females retain viable sperm in the lower portion of the oviduct for several months, and fertilized eggs are laid during the summer after mating.