ProphetM,
Thanks for the close up shots. I remembered that the tracks belonged to the Union Pacific and they were known as the Pasadena Branch. Here is a site I stumbled upon about it. The line ran from near Figueroa and Ave 19 in Lincoln Heights, all the way up to near Jet Propulsion Lab (JPL) on the east side of the Arroyo. Crossed Colorado Blvd in Pasadena, at about where the center divider of the 710 Freeway stub is today.
http://abandonedrailroads.homestead....sadena_br.html