Newsom's hybrid Chevrolet Tahoe was parked on Mission Street between 24th and 25th streets around 8:45 a.m. when a 14-Mission bus traveling south made "minor contact" with the SUV, Muni spokesman Judson True said.
The hit left a large black mark on the back, right side on the bus and broke the glass on the side of the mayor's vehicle, True said.
Newsom was inside a Spanish radio station office, being interviewed about his opposition to Proposition 8, mayoral spokesman Nathan Ballard said.
No one was inside the vehicle and there were no reported injuries. Only the specific bus experienced delays, True said.
