Will's Mammoth

``What did you do today, Will?'' ask a literal-minded mother and father. Their son replies, ``I rode my mammoth.'' Chronicling most of this boy's fantastic voyage in very few words and superb watercolors, Martin ( Foolish Rabbit's Big Mistake ) and Gammell ( Song and Dance Man ) evoke a prehistoric landscape vast in scope and ticklishly humorous in details: the long red tongue of a woolly rhino licks her offspring's bristly forehead; two mammoths play tug-of-war with an infant of their species; cave-dwelling humans build snow mammoths instead of snow men. But it is Will's mount that is most lovingly characterized: tough but tender-hearted, this nameless creature plods impassively through snowy vistas to pluck a flower for his rider. His goofy face, with sunken blue eyes and great, unfurling tusks, is sweet yet sad, a radiant invention in a small epic of the imagination. Working on a scale less domestic and with a palette less pastel than previously, Gammell equals or outdoes his fine earlier achievements. Ages 4-8. (Sept.)