Complex sentence: The pass was discovered by Edwin Harrison McHenry, a civil engineer working for the Northern Pacific Railway, who was tasked with locating a route for the NP from the main line near Logan, Montana through to Butte.
Split into simpler sentences: The pass was discovered by Edwin Harrison McHenry, a civil engineer working for the Northern Pacific. McHenry was tasked with locating a line from the NP's main line near Logan, Montana, through to Butte.