We decided to put a skin track in on West facing mineral across from GB NO to stay warm in the sun on Monday afternoon. Our initial concern was whether there would be a sun crust below the new snow, thinking the structure would be more consolidated and solar compared to other slopes we had skied. We were surprised to find very poor structure on the slope, with a pronounced density inversion starting 1 - 1.5 feet below the snow surface. My concerns about slope stability were confirmed with a whoomphing collapse, leaving a depressed margin above me where the slope had collapsed. We were able to ascend further on lower angled slopes, but chose not to ski the final rollover where the collapse had occurred by skiing into the tracked-up East Fork gully instead. A surprising end to three days of touring where we had not noticed obvious instabilities.