MFcr with weak faceting adjacent. In Sawtooths, this layer is present and looks similar on both NE and SE. So, not a sun crust, either an ambient MFcr (my hunch) or some sort of IFrc (less likely, but possible). Layer is 1-1.5cm thick, 1F to 1F+ hardness. On Butterfield there is no obvious crust at this interface on shaded slopes.
There is a band of dust closely associated with this interface, this has been found in Sawtooths, Galena Summit, and Butterfield. It appears to be buried a few cms below the actual 11/17 interface