As of July 2001, CalTrans has just started construction extending it from it's end at the San Dimas Interstate 10, California 57, and of course, Interstate 210 interchange to connect it to Interstate 15. Currently, it goes through the following:
Orignally it used to be only the part that goes around Devil's Gate Reservoir connecting La Canada Flintridge and Pasadena and until 1964 was known as California 118 before the great California Route Renumbering. The freeway everyone uses there is not the orignal. You can still see the reminants of the original, in fact some parts of the current I-210 have off-ramps to it. For some good pictures, check out http://www.scvresources.com/highways/foothill_fwy.htm