Dolerites mostly occur as single dykes. If however, they crosscut the surrounding rocks in large numbers they are called dolerite swarms.
This dolerite swarm is part of the so-called 'Giant's Playground' east of
Keetmanshoop in southern Namibia. It penetrated into the upper parts of the earth's surface about 180 million years ago and it's formation is associated with the initial break up of the Gondwana Continent.Text source: Namibia Fascination of Geology - Nicole Grunert
The strange looking trees in the pics are Quiver trees(Aloe dichotoma).