Arches National Park contains ephemeral pools, from a few inches to several feet in depth, that are essentially mini-ecosystems, home to tadpoles, fairy shrimp, and insects. The pools form among the sandstone basins, within potholes that collect the rare rainwater and sediment.There are more than 2,000 arches in the park; to be classified as an arch, the opening must measure at least three feet across. The largest arch in the park, Landscape Arch, spans 306 feet (longer than a football field) base to base. New arches are constantly forming, while old ones occasionally collapse—most recently Wall Arch, which fell in 2008.
About 300 million years ago an inland sea covered what is now Arches National Park. The sea evaporated and re-formed more than 29 times, leaving behind salt beds thousands of feet thick.Another unique aspect of the park is its knobby black ground cover, which is actually alive. A biological soil crust, it is composed of algae, lichens, and cyanobacteria (one of Earth’s earliest life forms), and provides a secure foundation for the desert plants.