What this photo actually shows is a stretch of the Libyan-Algerian border about 90 miles (140 km) south of Ghadames. Libya is on the left, Algeria is to the right, as if you couldn't tell for yourself!
Where my previous drilling photos were located near the center of Concession 20 and in the northern part, this one (I'm fairly sure from its sequence in my collection) is from the southern end of the concession.
This wadi had obviously seen some reliable moister over the years judging by the palm tree. There's also some scrubby bushes around. The surface also looks 'caked' rather than sandy or gravelly.