Eastbound lanes of the lower deck of the Bay Bridge were covered in sand and gravel for more than an hour this morning after CHP investigators believe a dump truck unloaded on the roadway and drove away.

The spill spanned 200 to 300 feet near the Treasure Island tunnel and was reported about 6:30 a.m. Sand piles as deep as eight inches were reported.

Motorists reported a sulfur smell as they drove near the spill.

Three lanes were closed until about 8 a.m., delaying eastbound traffic. Drivers reported taking as long as 50 minutes to cross the bridge.

It was not immediately clear how the spill had happened, and CHP reported no plans to conduct a search for the offending truck.