I definitely think that the mature mule deer bucks have harems during the rut!  Almost every mature buck I have harvested or seen durng the rut has been with several does.

The one I got in 2008 had several does with him and after I shot him, another, and bigger :( , buck came out of the ravine with his "harem".  He ended up immediately heading off with his new larger harem and was shortly followed by a couple of younger bucks.

While not in the rut, I believe that, for the most part, the mature bucks tend to go solo and the younger bucks tend to hang out in bachelor groups.

I meant to clarify one statement in my original post when stating that those mulies were similar to elk and antelope by having harems.  I don't know if elk and antelope have harems except when they are in the rut, however these mulies were clearly not in the rut yet still seemed to have harems of does with them.  I haven't quite figured it out.

Although mule deer bucks are many times seen with groups of does during the rut, even quite large groups of them, it is not the same behavior that you are seeing with elk. Mule deer bucks tend does as they go into estrus. The does and young bucks are already grouping up come late October. The bucks are not gathering a harem like bull elk are. They are simply tending does as they come into heat... and those does just so happen to many times be grouped up when this happens. The buck will follow a large group of does because there are many copulation opportunities at hand in one of these groups. Other bucks may come into close proximity when one of those does is close to go into heat. A fight might result. So these groups aren't true harems so to say.

As far as bachelor groups during the rest of the year... I have seen gigantic bucks in bachelor groups with small 3x3's. Not all of the biggest bucks are solitary year round although some might be. But for the most part, bachelor groups are pretty typical.

Good Post Hawkeye!  Your right on the money.  While antelope and elk will agressively defend their group of does or cows from other males, mule deer will be with does during the rut but are non committed to a certain group of does, rather they'll be committed to a doe or does in estrus and will fight to breed that doe or does.  If a group of does doesn't have one in estrus, the mule deer buck will travel on looking for a hot doe.

We were Mountain Lion Hunting on the White Mountain Apache Reservation in Arizona this past weekend (2/20) and bumped into a group of 16 Muleys.  One was a older thick 175 class deer with a slightly smaller 4 x 4 and two spikes.  They were packed up with 12 doe.  I'm obviously wrong, but I would've thought the bucks would breakaway after the rut.  I know whitetails that don't breed hit a second estrus cycle, possibly they were hanging around for that?

Most but not all of the bucks I have seen in the last couple of weeks have been alone or with a couple of other bucks.

 As far as the second cycle goes that should have happened in December. Far to late in the year for that now. Sometimes in heavy snow years I will see more of them pushed together but that's not the case where I live, at least for this year.