Keystone KornerDuring the 1970s, when jazz clubs all over America were folding under the onslaught of rock and roll and disco, San Francisco's Keystone Korner was an oasis for jazz musicians and patrons. Tucked next to a police station in the city's North Beach area, the Keystone became known as one of the most important jazz spots in the United States. It was so beloved by musicians that superstars McCoy Tyner, Freddie Hubbard, Ron Carter, and Elvin Jones played a