Camp 9. in the Great Sand Sea (about 60 miles WNW from Ain Dalla).
"We penetrated 15 miles in this way, working north or south along a range of dunes till a gap in the crests was found, and crossed six ranges before camping for the night on the top of a particularly large whaleback. ...
At the sixth range of sand the western descent was bad, even the touring car having to be pushed and dug downhill, so it was thought unwise to take all three vehicles any farther owing to the uncertainty of getting the lorries back up the west slopes.
Consequently one lorry and a quantity of stores were dumped at the top of the dune at Camp 9."
(R.A. Bagnold, Journeys in the Libyan Desert, 1929and 1930, The Geographical Journal, July 1931)