Across a broad plain on the island of Bohol in the central Philippines, more than a thousand rounded green mounds rise from the landscape in near-uniform cones, spread across the countryside like scattered scoops. For much of the year the hills are cloaked in grass, but as the dry season sets in the vegetation withers and turns a rich brown, and the whole field takes on the appearance that gives the formation its name. The transformation is seasonal, dependable and one of the most recognizable natural spectacles in the country.
More than a thousand near-identical mounds
Estimates of the number of hills vary, but they run into the thousands, with commonly cited figures ranging from roughly 1,260 to more than 1,700 spread across an area of several dozen square kilometres. According to Britannica, the mounds are grass-covered hills of limestone, generally between about 30 and 120 metres in height, and their remarkable regularity, cone after cone of similar size and shape, is a large part of what makes the field so arresting. The hills are concentrated in the interior of Bohol around the towns of Carmen, Batuan and Sagbayan, where viewing platforms let visitors take in dozens at once.
Why the hills turn brown each dry season
The color change that supplies the name is a matter of botany rather than geology. The hills are covered in grasses that stay green through the wet months but dry out as rainfall fades, typically later in the year, browning across the whole field at once. As Live Science notes, the shift is what earned the formation its chocolate-drop nickname, and it reverses again when the rains return and the grass grows back green. The hills are not piled-up soil but solid rock beneath their grassy skin, which is why they hold their shape year after year regardless of the season.
Limestone, uplift and long weathering
The hills are built from marine limestone, rock formed from the shells and skeletons of sea creatures deposited when the area lay beneath the ocean. Over roughly the last couple of million years, geological forces lifted that limestone above sea level, and tectonic activity fractured it. Rainwater, which is mildly acidic, then went to work dissolving the exposed stone along its cracks and weaknesses, a process that over vast stretches of time sculpted the fractured rock into the rounded mounds seen today. Geologists describe the formation, as summarized in resources such as GeologyScience, as the cumulative product of marine deposition, uplift, chemical dissolution and long-term surface erosion, a textbook example of how tropical weathering carves limestone into distinctive shapes.
From local landmark to global geopark
The hills’ scientific and cultural value has been formally recognized well beyond the Philippines. Bohol Island, with the Chocolate Hills as its centerpiece, has been designated a UNESCO Global Geopark, a status that highlights areas of international geological importance and ties their protection to local tourism and education. That recognition reflects how unusual the formation is: while cone-shaped limestone hills occur in other tropical regions, few places display them in such numbers and such striking uniformity across a single plain. The designation also brings scrutiny over how development around the hills is managed, a concern that has surfaced when resorts and roads have encroached on the protected landscape.
Legends and lasting protection
Long before geologists explained the hills, local folklore offered its own accounts, including tales of feuding giants who hurled boulders and mud at one another and left the debris behind, and a gentler story of a giant weeping over a lost love whose dried tears became the mounds. Today the Chocolate Hills are treated as a national treasure, declared a protected geological monument and promoted as one of Bohol’s leading attractions, drawing travelers who climb the viewing decks to watch the seasonal color sweep across the field. Whether green in the rains or chocolate brown in the drought, the formation remains a rare case of geology and botany combining to stage a landscape that visibly changes with the calendar.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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