THE RUNWAY SURFACE HAD BEEN GRADED, AND SOFT GRADED MATERIAL HAD BEEN PUSHED INTO A SMALL DEPRESSION ADJACENT TO THE RUNWAY. THE AIRPLANE WAS TAXIING BACK TO THE RAMP, WHEN THE NOSE WHEEL ROLLED INTO THE DEPRESSION AND THE NOSE GEAR COLLAPSED. THE SOFT AREA/DEPRESSION HAD BEEN PREVIOUSLY MARKED WITH YELLOW CONES. THE CONES HAD BEEN REMOVED WHILE THE RUNWAY WAS BEING GRADED AND HAD NOT BEEN REPLACED. NO NOTAMS HAD BEEN ISSUED. THE ALASKA SUPPLEMENT STATED THAT THE RUNWAY WAS SOFT AND RUNWAY CONDITIONS WERE NOT MONITORED.