Talmont is situated on a small piece of rocky headland that overlooks the biggest estuary in Europe, the Gironde. At Ambès, the Dordogne and the Garonne rivers meet to form this large body of water called the Gironde, which widens out onto the ocean. At high tide, waves roll up the length of the estuary, mixing with freshwater, while at low tide the river flows into the ocean.
Heading northwest along the large bay that connects Talmont to Meschers, cliffs increasingly dominate the shoreline, which is divided into a series of coves and inlets until reaching La Pointe de la Coubre, which marks the point where the estuary meets the ocean. The landscape as we see it today has been shaped by both natural and human activity.
The headland of Talmont was originally an limestone islet separated from the riverbank, at the centre of a wide bay spanning the distance from Merschers to Barzan. From the High Middle Ages onwards, the bay gradually filled with sediment, transported by the ebb and flow of the tides and deposited in this area close to the shore, where the waters were calmer. This created a siltation process, as can be seen today at the little cove of Caillaud, where the land is muddy and rich in vegetation. Grassy, reeded marshes eventually joined the limestone island to the old continent. These marshes were prone to flooding, and were drained during the late 18th century to create farmland. Marshland covers most of the area surrounding Talmont.