We left one our packs (red and grey Bullet pack) at the base of the descent gully while climbing Mithral. We couldn't find it on our way down - we'd left it under a big boulder with the biggest cairn at the intersection of the descent gully and the Fishhook/Mithral approach trails. Inside, there was a nalgene bottle and a BD spot headlamp. Don't think it was a marmot as we spent an hour or so looking for it that day and the next day when we went back to climb Fishhook.