RICHMOND -- Two trucks collided near the Richmond-San Rafael Bridge toll plaza Friday morning, causing one lane to be closed and backing up traffic for several miles.

The California Highway Patrol issued a severe traffic alert after the 8:10 a.m. wreck, which happened in the westbound direction of Interstate 580 approaching the toll plaza to the bridge.

The collision between a pickup truck and a flatbed truck spilled gravel and sand from the pickup onto the freeway, the CHP said. Caltrans workers were at the bridge and were cleaning up the gravel, which was in the far left lane.

Motorists were advised to avoid the area if possible, the CHP said. The lane was expected to be opened by 9:15 a.m., the CHP said.

Contact Rick Hurd at rhurd@bayareanewsgroup.com and follow him at Twitter.com/3rdERH.