Arches National Park.
Perched high above the Colorado River, the 76,359 acres Arches National Park, established on November 12, 1971, is part of southern Utah’s extended canyon country, carved and shaped by eons of weathering and erosion. Most of the formations at Arches are made of soft red sandstone deposited 150 million years ago. Much later, groundwater began to dissolve the underlying salt deposits. The sandstone domes collapsed and weathered into a maze of vertical rock slabs called “fins.” Sections of these slender walls eventually wore through, creating the spectacular rock sculptures that visitors to Arches see today. This Park contains more than 2,000 natural arches—the greatest concentration in the country. But numbers have no significance beside the grandeur of the landscape—the arches, the giant balanced rocks, spires, pinnacles, and slickrock domes against the enormous sky. To be classified as an arch, the opening must measure at least three feet across. The largest arch in the park, the Landscape Arch, spans 306 feet base to base (longer than a football field). New arches are constantly forming, while old ones occasionally collapse—most recently Wall Arch, which fell in 2008.
The land has a timeless, indestructible look that is misleading. More than 700,000 visitors each year threaten the fragile high desert ecosystem. One concern is a dark scale called biological soil crust composed of cyanobacteria, algae, fungi, and lichens that grow in sandy areas in the park. A biological soil crust, it provides a secure foundation for desert plants. But footprints tracked across this living community may remain visible for years. In fact, the aridity helps preserve traces of past activity for centuries. Visitors are asked to walk only on designated trails or stay on slickrock or wash bottoms.
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.
Credit: National Geographic Society