Officials say some asphalt came loose on the span Tuesday morning, following a paving project overnight.
The two most westerly lanes were paved Monday night as part of the the Seismic Retrofit project at the north approach. When cars began driving on them during the morning commute, the asphalt began to unravel leaving aggregate debris including pebbles on the roadway.
A portion of one southbound lane will closed until 11 p.m. Tuesday night to allow for repairs.
Anyone headed into the city is encouraged to leave earlier and expect delays.