Located in Marin County. This area, called West Marin by the locals, is included in the Golden Gate National Recreation Area.

The eastern shore of Tomales Bay rests on the American tectonic plate, and the western shore, the Point Reyes Peninsula rests on the Pacific tectonic plate. The San Andreas Fault Line runs down the middle of Tomales Bay. Scientists consider Tomales Bay one of the most pristine bays in America.

It is home to abundant fish and waterbirds. It is an area renown for oyster and abalone farms and great for canoeing and kayaking. Point Reyes Station lies at the south end, the throat of the bay, and Dillon Beach lies at the north end, the mouth of the bay. The town of Tomales, on Highway 1 (the Coast Highway), is a few miles inland from Dillon Beach.