The study found the western edge of San Francisco, along with Redwood City and the area around Santa Clara and Sunnyvale -- have rates of autism roughly twice as high as their neighbors.
They point out this is not due to pollution, or other environmental risks.
Rather, the clusters were correlated to neighborhoods with high education levels, or are near autism treatment centers.
Researchers at U.C. Davis have identified three pockets of the Bay Area that have higher rates of autism than anywhere else.