Metrolink already goes there. BLW station is supposed to be adjacent to the Metrolink RC station. With a bit more double tracking, ML might be able to run a 1/2 hour headway for trains at some times. Figure about an hour (maybe less for expresses or skip-stops) from LA to RC.

As for Gold Line - Bob? Since RC is in San Berdoo Co, and Gold Line is a LA Metro operation, seems unlikely that it'll get that far without some serious politicking and SBd funding. For a long time, realistically, your main options from Gold Line territory would be to either ride it to Union Station and grab a ML train to RC, or find a direct bus line, or drive/get a rideshare to RC (there almost certainly will be a good-sized garage).