This definitive biography offers a new critical assessment of the life, works, and ideas of Herbert E. Bolton (1870–1953), a leading historian of the American West, Mexico, and Latin America. Bolton, a famous pupil of Frederick Jackson Turner, formulated a concept—the borderlands—that is a foundation of historical studies today. His research took him not only to the archives and libraries of Mexico but out on the trails blazed by Spanish soldiers and missionaries during the colonial era. Bolton helped establish the reputation of the University of California and the Bancroft Library in the eyes of the world and was influential among historians during his lifetime, but interest in his ideas waned after his death. Now, more than a century after Bolton began to investigate the Mexican archives, Albert L. Hurtado explores his life against the backdrop of the cultural and political controversies of his day.