From July to November 1833, Joseph R. Walker led a brigade of fifty-eight fur trappers, with two hundred horses and a year's provisions, from the Rocky Mountains of Wyoming to the Pacific coast of central California. Toward the end of their journey the Walker brigade crossed the Sierra Nevada, becoming the first non-Native people to traverse the range from east to west. That crossing, made long and brutal by bewildering terrain and deep snow, is widely and rightly considered a milestone in the exploration of intermontane North America.

Following Walker's death in 1876, an...