sentences:  It is traversed by State Route 89 and lies on the boundary between Alpine County (in the Carson River basin) and El Dorado County (in the Tahoe area).The pass crosses a mountain spur that links the Sierra Crest, the main ridge of the Sierra Nevada to the southwest of the pass, with the Carson Range to the northeast.The pass is named after Ira M. Luther, one of the "Irish Brigade" described by Mark Twain in "Roughing It".