LOS ANGELES (AP).- Rock stars are a common enough sight in Los Angeles but it’s not often when a rock is the star. Los Angeles residents are coming out to catch a glimpse of a massive boulder that arrived at the Los Angeles County Museum of Art before dawn Saturday, after lumbering across Southern California for the past week and a half. It will become the centerpiece of acclaimed earth artist Michael Heizer’s latest creation, “Levitated Mass.” “The sheer size of it is just impressive. The size of the rock, and the size of the undertaking,” said Ron Dickson, 64, who drove down from Burbank. The 340-ton hunk of granite, accompanied by an entourage of about 100 people, left a dusty quarry in Riverside on Feb. 28, chauffeured toward its destination by a specially built carrier