Dorsal coloration variable; ground color may be cream, grey, red, or black. Dorsum may show a variable pattern of dark streaks and blotches. Head lacks tympanum, pupil is vertical, and a light streak may extend from tip of snout to above the eyes. Whitish-yellow venter, more yellow in femoral region. Males have a tail-like extension of the cloaca, and during breeding season show greatly enlarged forearms. Larvae have a distinctively large, round mouth, modified for suction, which they use to cling to streamside rocks (modified from Stebbins 1951).
 
Ascaphus is the only living representative of a basal lineage of anurans, and may retain some relatively primitive traits of early frogs (e.g. Ford and Cannatella 1992).

See another account at californiaherps.com.