The Hato Mayor Province was declared the first Eco-tourist province of the Dominican Republic, as it contains ecosystems of great value for the preservation of the country's biodiversity. The chain of mountains in the east and southeast is of young igneous or volcanic origin. The northern area are also rocks, but of much older age. Notable are also iron ore deposits in the northeast.
There are several areas of Cretaceous limestone, calcareous sandstones and clay schists, which are karstified. The caves of Fún-Fún and Doña Ana are the most well known in the Karst region of Los Haitises. the Miocene limestones of the Los Haitises National Park form an extensive karst platform of 1,600 km². It is characterized by conical hills of uniform height between 200 to 300 meters above sea level. There are many sinkholes which swallow the abundant rains of an annual average rainfall of over 2,500 millimeters. The Pie de Monte and the Eastern Cordillera or Sierra de El Seibo have metamorphic and sedimentary rocks. On its southern slope is a limestone belt where important caves were discovered. It is covered by humid tropical forest. Also the Southeastern or Caribbean coastal plain has Limestone or calcareous rocks, but as it is a low coastal plain there are no notable caves found.