i run for caltech. you can check out our runs at the link. most of them are just loops around the streets of San Marino. The arroyo is the best place in Pasadena I know to run, other than maybe the golf courses at night.
If you want to head up to the mountains there are plenty of good runs. Starting up by JPL you can check out the "JPL" and "Millard Campground" runs listed on the site. "Patrician" is also a pretty good run that takes you up in the hills West of the Rose Bowl and is very scenic and peaceful i guess.
It might be closed right now, but the Mount Wilson Toll Road at Eaton Canyon is good. so is the Mt Wilson Trail. There's a handy book called "Trails of the Angeles" that describes lots of the trails up there. personally i hate the f***ing mountains and only run up there when people make me.
Lacy Park in San Marino is nice for a big grass field, or you can use the athletics fields down by the Rose Bowl. Also in San Marino, Huntington Dr and Sierra Madre Blvd both have nice, grassy median strips for running.
and if you want a track, oxy's is super fast