A buttress dam is a type of dam that uses a series of sloping supports, or buttresses, to hold back water. These structures are typically made of concrete and are designed to transfer the weight of the water to the foundation. Buttress dams are often built in narrow canyons where the rock can provide strong support. Unlike gravity dams, which rely on their weight to resist water pressure, buttress dams are more efficient in material use. They can be taller and thinner, making them suitable for locations with limited space. Common examples of buttress dams include the Hoover Dam and the Shasta Dam.