What I missed yesterday when reading your first post was the height of the crash site. Started a search for and found it in here:
Crash: Ace Air B190 near Dillingham on Mar 8th 2013, wreckage found
They obviously were indeed at the low altitude of 2000 ft which was part part of their clearance from ATCC Anchorage. Aside of what is apparently ATC responsibility the question remains: why for heavens sake the crew descended so low with all the information on the approach charts at hand ??
Hopefully not another case of over confidence in the magic words "identified, Radar contact" and the mentally wrong expectation of flying safe if only the instructions are followed.