Me and my wife went here this october. You have to park in the residential area, walk 3-5 mins to shasta retreat, trespass religious group area (just be quiet when trespassing them then you will see a bridge then you will see the railroad track. The railroad track has a lot of gravel so it is difficult to walk. There is like a natural man made route because people goes on the side so the gravel tends to be leveled. Keep an eye and listen for the train! Walk about a mile then you will see a bridge, look at your right and you will see the beauty of Mossbrae falls!
Tip: If you're going here from another county spend at least 2 days and do a waterfall marathon. Here is the option day 1 hedge creek falls, mossbrae falls, 3 mc cloud falls. Sleep in a motel then burney falls!
Here is a video of our waterfall adventure.
https://www.youtube.com/watch?v=PcYezvmM0Bs