Botswana's illusive Deception Valley is all that remains of a sprawling riverbed that has long since dried up. Stretching across 80km of the park's north, the valley is now covered with short grass, and dotted occasionally with small islands of bushy trees. Some of the roots of the larger trees extend as far as 50m below the surface to the water table, enabling them to survive the harsh dry winters. The low canopies of the tree grove islands, usually made up of umbrella thorn (Acacia tortilils) and buffalo thorn (Ziziphus mucronata) provide shelter for game during the heat of the day and one can often also see prides of lion dozing in the shade of these thickets. The fossil valley was first brought to the world's attention in 1985, by the book 'Cry of the Kalahari' written by Mark and Delia Owens, who lived on the pan for seven years studying the brown hyena that live here.