The Chocolate Hills are an unusual geological formation in Bohol, Philippines.According to the latest accurate survey done,there are 1,776 hills spread over an area of more than 50 square kilometres (20 sq mi). They are covered in green grass that turns brown during the dry season, hence the name.
The Chocolate Hills are a famous tourist attraction of Bohol. They are featured in the provincial flag and seal to symbolize the abundance of natural attractions in the province. They are in the Philippine Tourism Authority’s list of tourist destinations in the Philippines; they have been declared the country’s third National Geological Monument and proposed for inclusion in the UNESCO World Heritage List.
The vegetation of the Chocolate Hills is dominated by hard grass species such as Imperata cylindrica and Saccharum spontaneum. Several Compositae and ferns also grow on them. In between the hills, the flat lands are cultivated with rice and other cash crops. However, the natural vegetation on the Chocolate Hills is now threatened by quarrying activities.
The Chocolate Hills are conical karst hills similar to those seen in the limestone regions of Slovenia, Croatia, northern Puerto Rico, and Pinar del Rio Province, Cuba. These hills consist of Late Pliocene to Early Pleistocene, thin to medium bedded, sandy to rubbly marine limestones. These limestones contain the aboundant fossils of shallow marine foraminifera, coral, mollusks, and algae. These conical karst hills, called mogote, are created by a combination of the dissolution of limestones by rainfall, surface water, and groundwater and their subaerial erosion by rivers and streams after they had been uplifted above sea level and fractured by tectonic processes. These hills are separated by well developed flat plains and contain numerous caves and springs. The Chocolate Hills are considered to be a remarkable example of conical karst topography.
The origin for the conical karst of the Chocolate Hills is described in popular terms on the bronze plaque at the viewing deck in Carmen, Bohol. This plaque states that they are eroded formations of a type of marine limestone that sits on top of hardened clay. The plaque reads:
The unique land form known as the Chocolate Hills of Bohol was formed ages ago by the uplift of coral deposits and the action of rain water and erosion.
The plaque also makes reference to a fanciful explanation of the origin of the Chocolate Hills that is unsupported by any published scientific research, i.e. either Hillmer or Travaglia and others, when it states::
the grassy hills were once coral reefs that erupted from the sea in a massive geologic shift. Wind and water put on the finishing touches over hundreds of thousands of years.
Self-published, popular web pages present a variety of fanciful and less credible explanations about how these hills formed. They include sub-oceanic volcanism; limestone covered blocks created by the destruction of an active volcano in a cataclysmic eruption; coral reefs that were raised from the sea as the result of a massive geologic shift; and tidal movements.  The lack of any exposed or associated volcanic rocks anywhere in the Chocolate Hills refutes the popular theories involving volcanic eruptions. These theories involving either a sudden, massive geologic shift, coral reefs being erupted from the sea, or tidal movements lack any collaborating evidence and support among geologists.
Four legends explain the formation of the Chocolate Hills. The first tells the story of two feuding giants who hurled rocks, boulders, and sand at each other. The fighting lasted for days, and exhausted the two giants. In their exhaustion, they forgot about their feud and became friends, but when they left they forgot to clean up the mess they had made during their battle, hence the Chocolate Hills.
A more romantic legend tells of a giant named Arogo who was extremely powerful and youthful. Arogo fell in love with Aloya, who was a simple mortal. Aloya’s death caused Arogo much pain and misery, and in his sorrow he could not stop crying. When his tears dried, the Chocolate Hills were formed.
The third legend tells of a town being plagued by a giant carabao, who ate all of their crops. Finally having had enough, the townsfolk took all of their spoiled food and placed it in such a way that the carabao would not miss it. Sure enough, the carabao ate it, but his stomach couldn’t handle the spoiled food, so he defecated, leaving behind him a mound of feces, until he had emptied his stomach of the food. The feces then dried, forming the Chocolate Hills.
The last legend is about a gluttonous giant named Miguel that eats everything in his path. One day he came to a plain. He saw a beautiful young woman named Adrianna. To win her affection, he needed to lose weight. So he excreted everything he ate. In the end, his fecal matter covered the land and he won Eng’s affection.
Read more at Source:http://en.wikipedia.org/wiki/Chocolate_Hills