Beaver Street Wall at 185 Beaver Street, San Francisco, California.

If the word slickenside is not part of your everyday vocabulary, you must make it so immediately. The word is almost as awesome as the thing itself.

This is an amazing piece of geology right in the middle of San Francisco. More than a few years ago, this was deep underneath the Earth and part of the Corona Heights Fault. The diagonal lines show the direction of the fault slip. You can even see places where the sedimentary layers buckled. The wall is made of chert. In some places this wall is as slick and shiny as glass. A translucent layer of silica called silica gel, is what makes this wall so darn shiny. Apparently chart is filled with silica so the tremendous pressure and friction the fault movement transforms it into a glassy surface that coats the rock. Is that awesome or what?