A truck dumped a payload of mud and sand all over the Treasure Island exit ramp off the eastbound span of the Bay Bridge early Thursday, officials suspect, and then left the scene — triggering a traffic slow-down headed to the East Bay. Crews were working to clear the ramp of silt, but officials don’t know when it will re-open, according to Officer Vu Williams, a California Highway Patrol spokesman. While Caltrans crews used heavy machinery, including front-end loaders, to clear the grit from the road, the CHP was looking for the trucker suspected of causing the mess.