Hey,
I'm in Sandy as well and do a ton of riding (approx 20 hrs week). I usually go to Five Mile as I believe it's the best, least crowded, and offers the most variety. It is fairly extensive so keep your bearings or you could get lost easily. Especially Sunshine Canyon and up to the top. Deele is very similar but tends to be wall to wall weekend wallies Friday thru Sunday. The knolls rocks. Far better than Sahara and firm enough sand that you don't need a paddle.
As one of the other posts indicated A.F. canyon can be nice, but unless you're on a thumper you will need to re-jett, sometimes on the side of a trail at upper elevations. Also make sure you have an approved spark arrestor or you will be fined.
One other thought: The flats east of Saltair can be good if your looking for a quickie after work. Not much terrrain features though and only 2 little kickers. It's good for wide open running or checking repais for sure and only about 20 minutes from us(light traffic, if that ever happens anymore)
If you have any other ?'s hit me back. By the way, where in N. Cal were you. I lived in Santa Rosa for a while myself. Nice area. I am bringing my bike back there over Christmas and was wondering if you could suggest some good areas that are still open. KEEP ON ROOSTIN!!!