Its volcanic material is Aeolian ash, weathered tuff and basalt. Rhyolite flows intruded along faults in the Smith Rock Tuff. Examples of pyroclastic rocks are tuff and ignimbrite. I sediments above the basalt consist of layers of Olmoti tuff and lake sediment claystone. The Cuchivero Group consists of ash flow tuff and granitic plutonic rocks. They consist of metamorphosed graywacke, argillite, tuff, mafic igneous extrusive flows, and carbonate rock. Basaltic tuff or pyroclastic rocks are rare but not unknown. Explosively erupted pyroclastic material is called tephra and includes tuff, agglomerate and ignimbrite. The top layers are made up of tuff and lava material. It was followed by the Mesa Falls Tuff and the Lava Creek Tuff eruptions. Some volcanoes were explosive with bombs, and pyroclastic tuff. Predominant rock types include shale and graywacke, with greenstone, tuff and chert. The volcanic tuff cone is a State Monument. This is a coarse ash crystal tuff containing lapilli. The Church of Saint George was carved downwards from a type of volcanic tuff.