Incidents of cannibalism always make for intriguing, if not morbid, true life tales, and the granddaddy of them all is the story of the Donner Party. This definitive volume fills in the details of that doomed voyage, drawing on diaries of the few surviving pioneers who struggled through the desert only to find themselves trapped in the snows of the Sierra Nevadas. Don't be deterred by the subject matter, this book is much more gripping than gruesome.  (USW414, $14.95)