Sandstone Fins, Arches National Park, Utah, Postcard

Afternoon clouds roll in over sandstone fins in Arches National Park in eastern Utah. Arches National Park lies atop an underground salt bed, which is the main cause of the formation of the arches and spires, balanced rocks, sandstone fins and eroded monoliths in the area. To create fins, erosion occurring within the cracks wears away exposed rock layers and enlarges the surface cracks isolating narrow sandstone walls. Arches is known for preserving over 2000 natural sandstone arches, including the world-famous Delicate Arch, in addition to a variety of unique geological resources and formations. The park is located just outside of Moab, Utah, and is 119 square miles (310 km2) in size. Its highest elevation is 5,653 feet (1,723 m) at Elephant Butte, and its lowest elevation is 4,085 feet (1,245 m) at the visitor centre. Forty-three arches have collapsed due to erosion since 1970. The park receives 10 inches (250 mm) of rain a year on average.