Dow crag rhyolite. Red-hot rocks. 

Dow is a great climbing venue - the compact rhyolite makes for great anguler holds and fine crack lines, when it isn't too wet or polished. But did you know the quality of the rock is all due to the type of eruption which formed them? Rhyolite is very high in silica, which makes the magma very viscous. It is also a very water-rich magma - these two facts make for massive explosive eruptions. The ash clouds which form in these eruptions are still red hot when they land (pyroclastic deposits) and hot enough that the rock is still partially molten. So the ash particles stick together to form a very strong and hard welded tuff. This block on the walk in to the crag shows several nice bits of evidence for the ductile nature of the ash when it was deposited - fiame (squished pummice bits), differential weathering of larger clasts, and rheomorphic features (evidence of post-emplacement flow).