The northern most pass and highest pass is Music Pass . It is located out of view behind Mount Herard, the flat-topped mountain to the north of the dunes. Because of its height and location, Music Pass probably has the least effect on the dunes. Medano Pass is the middle pass, visible in front and to the right of Mt. Herard. The windward face has a gradual slope.
Sand blown from the windward face is deposited on the steeply sloping leeward side.
Sand on the leeward side or slipface is subject to constant change, avalanching when the sand reaches its maximum angle of repose, at 34 degrees. Impossible as it may seem, no slipface can exceed a 34 angle. Although the wind typically blows from the southwest, occasional violent storms also blow in from the northeast. These winds can blow the sand on the crests and ridges of the sand dunes in a reverse direction, looking as if the ridge tops had folded back on themselves. Magnetite, a volcanic mineral originating from the San Juan Mountains, shows itself as black streaks in the sand is readily attracted to a magnet.