Here's an interesting article on Eagle Mountain: https://www.sfgate.com/travel/article/eagle-mountain-california-ghost-town-18096768.php . Riverside R2 ran to Eagle Mountain, being defined as Kaiser Road from Route 177 to Eagle Mountain (11.26 mi).
I went up that way in 2011 hoping to get some photos of the town. It had already been fenced for awhile by then and I didn't get to reach much from R2.
Never found an R2 shield anywhere on that route.
I just noticed that Google aerial imagery shows the rail line that used to service the mine was ripped up sometime between 2016 and 2020, all the way down to about -115.62 latitude, alongside the Bradshaw Trail. Maybe surplus rails suddenly became valuable again.