I pulled up
CalTopo and was surprised to see a trail going through the cliffs as you describe. I’ve never seen anyone go that way, though I’m sure that there is a way though the cliffs. There is a use trail that goes toward UBSL and then heads ~SW and then W to a point just N of the moraine. From there it goes N or NW to decent camping S of Iceberg Lake. The easiest way to the MR is to follow this use trail.
