The Three Lands are dominated by volcanism and, to a lesser extent, by the subduction of an oceanic plate to the east (the resulting mountain uplift is shown by a dotted line.)

Magmatic pressure resulted in the uplift of the three plateaux shown and has led to major rivers flowing along the faults between them.

The first diagram shows the basic geology:

[L] the limestone plateau of the Guarded Land which is on average 1000m above sea level. Because this is porous there is little or no surface water.

[U] the sandstone plateau of the Earthsky which is on average 500m above sea level. Being non-porous, lagoons tend to collect in depressions and then evaporate during the long dry season.

[S] a southern extension of the Earthsky plateau, separated from it by the valley of the Blackwater [river b].

Another river [r] runs in the much deeper gorge that runs in the fault between the Guarded Land and the Earthsky plateau and which opens into the Leper Valleys.

The second diagram shows the line of most extreme volcanism which bisects the Guarded Land plateau and which, running south, results in the 'Backbone' or extruded basalt dyke which runs down the western edge of the Earthsky. The same volcanism that forced the uplift of the Earthsky plateau finds expression in the koppies which are more basaltic extrusions, though this time vents.

Of note is the Isle of Flies in the Upper Reach [shown as a blue circle] which is a result of the Blackwater eroding down into the basalt dyke of the Backbone.

Most noteworthy of all is the Osrakum volcanic system [shown as an orange circle] which is where the magma causing the uplift of the Guarded Land plateau broke through to the surface in a sequence of volcanoes, the greatest being the massive cinder cone that collapsed to form the Osrakum caldera.