ontier career of Don Juan de Oñate, the first colonizer of the old Spanish Borderlands. Born in Zacatecas, Mexico, in the mid-sixteenth century, Don Juan was the prominent son of an aristocratic silver-mining family. In 1598, in his late forties, Oñate led a formidable expedition of settlers, with wagons and livestock, on an epic march northward to the upper Rio Grade Valley of New Mexico. There he established the first European settlement west of the Mississippi, launching a significant chapter in early American history. In his activities he displayed qualities typical of Spain's sixteenth-century men of action; in his career we find a summation of the motives, aspirations, intentions, strengths, and weaknesses of the Hispanic pioneers who settled the Borderlands. Marc Simmons holds the M.A. and Ph.D. degrees from the University of New Mexico. His publications include more than one hundred articles and nearly two dozen books on the American Southwest, several of them award winners.