Oh Boy! Ha!
I have not done what you describe, but i have looked at it on maps, and thought that a better way to get from the MCJO to the Whitewater might be to go up Galena then follow the ridge that makes up the southern boundary of the drainage you describe, though (like most of the potential routes to whitewater from the north) that looks like it gets pretty steep right above the Whitewater.
I don’t know of anyone having done this or having gone right down the drainage you mention. It would be really cool to discover that someone has done this. I’d really think the drainage itself would be a mess of deadfall and loose rock, though none of it looks terrible on topos or satellite imagery until you get to the bottom, which is kind of inconvenient. ha!
It’s not the same thing, but going from forest falls up the MCJO and across to (and down) the Middle Fork (of the Whitewater) Jumpoff (and back, in a day!) has been done (somewhat famously) by Pi, who was stalked by lions at the middle fork JO: https://www.flickr.com/photos/pitownpi/albums/72157624576684691
I wrote him about the route once, and he told me you’d have to be insane to attempt it. Ha!
I’m thinking about trying a new (to me) route up gorgonio from above the jumpoff this sunday. If i get up there, i’ll look down the south/east fork and let you know what i see.