We geologists will say it's an erosional feature, due to the Scabland floods, from a single thick basalt flow. The blocky, somewhat lighter part below is in the lower part of the flow, which cooled more slowly, while the more spindly buttes above are basalt that cooled from the surface and thus more quickly. The cooling fronts met in the middle of the flow, so that what looks like two flows is in fact a single flow with very different textures from the different cooling histories.
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slgwv said:
www.ipernity.com/doc/289859/33009659/in/album/438843
We geologists will say it's an erosional feature, due to the Scabland floods, from a single thick basalt flow. The blocky, somewhat lighter part below is in the lower part of the flow, which cooled more slowly, while the more spindly buttes above are basalt that cooled from the surface and thus more quickly. The cooling fronts met in the middle of the flow, so that what looks like two flows is in fact a single flow with very different textures from the different cooling histories.