22 Dunes Turning to Sandstone

In simple terms, the angle of repose is maximum angle at which any material can be piled before it shifts and falls.  For dry sand that angle is about 30 degrees, but these dunes exceed it.  The trick is that water in the sand helps bind the granules together – a trick every sand castle builder knows, though in this case the water comes from the snow melt feed creeks and gets absorbed in to the sand, rather than being dumped on it from a bucket.  Of course this sand stacking action places extreme pressure on the lower levels of the sand, so little by little that sand is turning to sandstone.  In another couple of hundred million years or so, the sand itself may be gone, so good thing we saw it now.