THIS SIXTEENTH-CENTURY odyssey of Cabeza de Vaca's is one of the great true epics of history. It is the semi-official report to the king of Spain by the ranking surviving officer of a royal expedition to conquer Florida which fantastically miscarried. Four out of a land-force of 300 men--by wits, stamina and luck--found their way back to civilization after eight harrowing years and roughly 6,000 miles over mostly unknown reaches of North America. They were the first Europeans to see and live to report the interior of florida, Texas, New Mexico, Arizona and northernmost Mexico; the 'possum and the buffalo; the Mississippi and the Pecos; pine-nut.