A Marin County technology executive was arrested on suspicion of assault with a deadly weapon after he got off his bicycle and beat a motorist unconscious during an alleged act of road rage in Mill Valley, a city police official said. The alleged attack occurred in the evening at the busy intersection of East Blithedale Avenue and Camino Alto. According to police, Smock and the motorist were at odds over whether the truck's mirror had struck Smock's bike as both men traveled along East Blithedale.