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The plateau of the Cypress Hills area is what's known as an erosional plateau, formed by millions of years of sedimentary deposits followed by millions of years of erosion. The hills reach their highest elevation, 1466 metres, at Head-of-the-Mountain, then gradually drop back to the plains of the south.

If you were to slice through the plateau, you would see layer after layer of different types of rock. The geological history of the area begins more than 70 million years ago, in the Cretaceous Period, when a warm, shallow sea covered most of the area called the Bearpaw Sea. Many rivers flowed into the sea carrying silt and clay, which was then deposited on the bottom and compressed into a flaky, dark grey shale, now known as the Bearpaw formation. This is the bottom layer of rock supporting the plateau. The Bearpaw Sea later withdrew, and with every change in the land and waters flowing over Cypress Hills came a new layer of sediment. Fossils can be found in many of the layers, including fossils of marine mollusks, dinosaurs and strange and extinct mammals such as sabre-toothed cats and camels.

Over the years, waters flowed around the plateau and eroded the grounds around it, making it stand up even higher above its surroundings. During the Ice Age, glaciers flowed around the Cypress Hills plateau without ever fully engulfing it. The top 100 metres of the plateau were left as an island, while the surrounding land and lower portions of the hills were carved and eroded by the ice sheets. When the ice melted, meltwater coursed between the plateau and the retreating ice, carving out the valleys that dissect many parts of Cypress Hills.

Even today, the hills continue to change shape and size. Water, from streams and sudden thunderstorms, erodes some of the land, deepening the coulees and ravines. Land is falling away at the outer edges of the plateau too, through slumping and occasional small landslides.