The so-called " Rochlitzer Porphyr ", a rhyolitic tuff, which makes up a large part of the mountain, was formed from deposits of late explosive eruptions of a volcano about 250 million years ago.
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Most of the sediment that makes up the layers in this formation was stream-laid ( Dibblee 1968 : 28 ), but there is a white layer of rhyolitic tuff ( sometimes called " marker tuff " ) near the top ( Dibblee 1967 : 86 ).
