San Pablo Creek
The NBI database says there is an arch under this section of freeway for the passage of San Pablo Creek. Short of feigning a vehicle breakdown there is no way to stop and check what is actually the design under the freeway.
Photo taken by Craig Philpott in April 2010
BH Photo #161618
You can pull up Bing's Bird's Eye View and get a rough idea of what's under there. Looks like a glorified culvert.