San Francisco is also famous for Alcatraz Island, the site of Alcatraz Prison, which - you guessed it - is made up of Graywacke! Graywacke is the result of turbidity flows that are most often caused by Earthquakes. The Alcatraz Terrane is bounded by a roughly diagonal line from near the foot of the San Francisco anchorage of the Golden Gate Bridge to approximately Pier 48 in China Basin. Graywacke is also found in the San Bruno Terrane in the South West part of San Francisco.
If you continue North from the posted coordinates, each successive intersection will provide another interesting view of Telegraph Hill and the Alcatraz Terrane. At the intersection of Sansome and Filbert, you will find a set of stairs that leads up to the top of Telegraph Hill, the home of San Francisco's Wild Parrots of Telegraph Hill!
To log this EarthCache: On the North West corner by the coordinates is a commemorative plaque unrelated to the earthcache, send an email to me with some facts from this plaque (proves you were there). Post the number of people in your group and some comments on your experience - for example, what do you see that gives you some indication of the strength/weakness of Graywacke (shows you thought about your visit)? You might want to post a picture!