Two lanes of traffic eastbound on the Bay Bridge are blocked after a big rig stalled Saturday afternoon, officials said. A report at 2:20 p.m. said a big rig was stuck and blocking the off-ramp to Treasure Island, said Officer Andrew Barclay, a spokesman for the California Highway Patrol. The incident has caused the two left lanes at the Treasure Island exit to be blocked off, backing up freeway traffic through San Francisco. Hamed Aleaziz is a San Francisco Chronicle staff writer.