The Pasadena Subdivision is the remnant branch line of the former Atchison, Topeka & Santa Fe Railway (AT&SF) Los Angeles Second District. The line currently branches off of the Metrolink San Bernardino line at CP Cambridge in Claremont. The line follows a generally east–west alignment, passed through the cities of Claremont, Pomona, La Verne, San Dimas, Glendora, and Azusa before coming to a truncated end in Irwindale. For most of its length it shares the corridor with the Metro L Line. Recent construction, known as the Foothill Gold Line Extension Phase 2B, as seen the tracks out of service west of San Dimas for most of 2021.