The salt of the Salt Shore, almost certainly an evaporite deposit, suggests that the region south of the Red Mountains, known as Dorne, was once submerged beneath a shallow sea. Some time in the past, sea level was lower as glaciers trapped water as ice. As sea level fell, a large depression, like the mouth of a leviathan, isolated itself from the adjacent ocean. The result was an entrapped body of briny water exposed to the solar radiation (or perhaps to the heat of dragon’s breath, as we are unsure of the evolutionary history of dragons). Over time, the sea began to evaporate away, leaving the salt behind (similar to the Bonneville Salt Flats near Salt Lake City, Utah). The age of these deposits is somewhat difficult to constrain. Evaporite deposits tend to form in hot, arid environments. As previously mentioned, desert environments tend to form near 30°. As will be discussed in the forthcoming sections, Westeros has gradually moved north throughout its evolution. Given this tectonic drift, we speculate that the Salt Shore deposits are approximately 30-40 million years old.
Additional geologic evidence supports this apparently brash claim of entire sea boiled away by the sun (or, again, dragons). If town names are to be trusted as geologically accurate (a dubious, but necessary assumption), then we can infer the presence of green sandstone at the island of Greenstone. Greenstone is a generic and generally unhelpful term, as it can apply to sedimentary or metamorphic rocks. Combing through references to greenstone on Earth yielded a hit in the United Kingdom, where greenstone refers to sandstone contaminated with emerald-hued micas that was deposited within a shallow sea. The geographic proximity of two separate rock types, greenstone and salt, consistent with shallow sea deposition strengthens the notion of a long lost sea. The final piece of evidence comes from the town of Sandstone (guess which rocks we assume are there). While sandstone can form in a variety of environments, we interpret these sandstones as deltaic, forming as rivers flowing from the Red Mountains reached the shallow sea and deposited their sediment load.