Folks have probably written this up before but I thought I mention it for current conditions.
I had been staying with some friends in Mammoth in mid Sept 2012 whilst they dirt biked around (I myself can't ride now
). I decided since the weather was clement I'd head over to the Whites, since I like the desert views better than the Sierra side of the Owens Valley. I thought I'd do Wyman Canyon, not having done it before, and since I love camping in the Whites.
Most descriptions say it's a fairly easy drive, just some bumps and occasional water crossings, which for the most part is true. Quite narrow in the canyon, which means you'll pin stripe your van a bit, and the passing can be sketchy. But I only passed one other vehicle (it was a Thursday), and saw one parked just east of Roberts mine.
Most descriptions I've seen also are from the top down; I guess most come up the paved road to the Whites or up Silver Canyon. That is definitely easier. Here's why: in the narrows area the road follows the bottom of the canyon, and is crossing or in the stream. Even though water was low, the stream had relatively recently jumped its normal course and streamed into the road, just above the falls. There were consequently a couple of ruts that other users had helpfully stacked with rocks, otherwise they'd be too deep to negotiate. These are generally easier to descend. When going up, you are accelerating up the hill from the trough in the stream bottom, so your tires are wet, prone to spin, and very good at spewing the necessary rocks from the ruts. Which consequently drops you into said rut, with unfortunate results. I bent some underparts that way. It's hard to slow crawl up because sitting with your rear in the water isn't a good idea either. Going down, however, you just roll over with no throttle and the rocks tend to roll under your wheels, kinda like boot skiing scree.
So...if you're up there soon (and I'd recommend it) try going down instead of up.
And BTW, although I didn't do it this time, Silver Canyon is also a hoot. I'd recommend going UP that. A pretty heavy SMB can go down without brake issues if you use 4WD low range, but the issue is the tight switchbacks. Not as tight as some in Silverton/Ouray, but kinda tight. It's always easier going UP tight switchbacks with a turning-challenged vehicle because you go wide INTO the hill and UP, which means you just roll back to where you started to try again. If you go wide going DOWN you end up at the edge of the precipice, which is OK UNLESS you don't have enough traction to back up...then you are royally (and scarily) stuck.
Here's the waterfall and the first rut; the second was worse.
And the stream in more bucolic repose: