The San Pablo Bay Trail is a flat and fast, with beautiful views of the San Pablo Bay from beginning to end. Perfect for beginners looking for a gentle introduction running on dirt, the San Pablo Bay Trail is also perfect for advanced runners looking for a flat, fast route for sprint or interval workouts. This run is located on Mare Island, just off of highway 37. It is easily accessible from Napa, Sonoma, or the Vallejo/Richmond area. The route begins at the San Pablo Bay Trail parking lot at the end of Dump Road (a gravel road which is an extension to the west of A St. at the intersection of Azuar Dr.) The run leaves from the parking lot along the main wide trail route, heading West then gently bending South along the San Pablo Bay shoreline for another 2 miles. At the end of the trail you will come to a turnaround. Take a moment to observe the wetland wildlife and the Carquinez Bridge before returning on the same route. Source