Just wanted to let everybody know, White Mesa is rather snowy right now, but still perfectly ride-able.
Went out there today with a couple of friends. There were snow bluffs pretty consistently, usually a couple inches deep, but we could ride through almost all of them, and it was plenty cold enough to be just snow, no mud. It was a fun added element to the ride, not wrecking in the snow.
So, if you are looking for a ride for the weekend, head on out. It's a classic winter mtb route.