The Chocolate Hills are conical karst hills similar to those seen in the limestone regions of Slovenia, Croatia, northern Puerto Rico, and Pinar del Río Province, Cuba. They probably started as corals growing in a warm, shallow sea about two million years ago. The hills consist of sandy to rubbly marine limestones. These limestones contain abundant fossils of foraminifera, coral, molluscs, and algae. These conical hills were created by limestone dissolving in rainfall and groundwater. There was erosion by rivers and streams after they were lifted above sea level. The hills are separated by flat plains and have numerous caves and springs. The Chocolate Hills are a remarkable example of conical karst topography.