Heavy fog appears to have factored in a domino-like chain of crashes that forced the closure of eastbound traffic on Highway 37 in Sonoma this morning, the California Highway Patrol said.

The crashes were first reported at 7:55 a.m. east of Skaggs Island Road, past the Second Napa Slough. Office Diana McDermott said 11 collisions involving 31 vehicles -- including a motorcycle and two big rigs -- prompted authorities to summon a fleet of 10 tow trucks and enlist the aid of Caltrans to bring electronic signs and barriers to divert traffic.

Eastbound traffic in the area was rerouted to Highway 121 toward the Infineon Raceway, and motorists were advised to avoid the area and consider the Richmond-San Rafael Bridge as an alternate route.

Four people were taken to the hospital, including a motorcyclist who suffered major injuries, McDermott said. The other injuries were described as minor.

The road was opened just before 11 a.m. but motorists should expect residual delays in the area.