Route through Riverside-Corona, CA

I'm planning a ride from San Bernardino to Huntington Beach via the Santa Ana River Trail. I've ridden both ends of the trail many times. There's a section between Riverside and Green River that is not complete. I assume the route there will have to be city streets. Anyone familiar with a good route connecting the two ends of the trail? I'll be on a mountain bike, so I don't have to have pavement. Any information is appreciated.