The trail to the left goes up to the Grand Ditch and the trail to the right goes up to Little Yellowstone.  However, if you look on the map you can take the trail to the left and, once it crosses the Colorado River, there is another split in the trail where you can head up to the little Yellowstone (and on to Poudre Pass).  That's the way I went.  I think.  Pretty sure.  I think I came back the other way and stayed high above Lulu City.  Oh well, just get a map (or, look at the one on my other web site) and it will be all clear.