The precipitation of iron oxides also formed laminae, corrugated layers, columns, and pipes of ironstone within the Navajo Sandstone. Being harder and more resistant to erosion than the surrounding sandstone, the ironstone weathered out as ledges, walls, fins, "flags", towers, and other minor features, which stick out and above the local landscape in unusual shapes. Age and history of investigation The age of the Navajo Sandstone is somewhat controversial. It may originate from the Late Triassic but is at least as young as the Early Jurassic stages Pliensbachian and Toarcian. There is no type locality of the name. It was simply named for the 'Navajo Country' of the southwestern United States. The two major subunits of the Navajo are the Lamb Point Tongue (Kanab area) and the Shurtz Sandstone Tongue (Cedar City area). The Navajo Sandstone was originally named as the uppermost formation of the La Plata Group by Gregory and Stone in 1917. Baker reassigned it as the upper formation of Glen Canyon Group in 1936. Its age was modified by Lewis and others in 1961. The name was originally not used in northwest Colorado and northeast Utah, where the name 'Glen Canyon Sandstone' was preferred. Its age was modified again by Padian in 1989. A 2019 radioisotopic analysis suggests that the Navajo Sandstone formation is entirely Jurassic, extending for about 5.5 million years from the Hettangian age to the Sinemurian age. Depositional environment The sandstone was deposited in an arid erg on the Western portion of the Supercontinent Pangaea. This region was affected by annual monsoons that came about each winter when cooler winds and wind reversal occurred. Outcrop localities Navajo Sandstone outcrops are found in these geologic locations: Colorado Plateau Black Mesa Basin Great Basin province Paradox Basin Piceance Basin Plateau Sedimentary Province San Juan Basin Uinta Basin Uinta Uplift Uncompaghre Uplift The formation is also found in these parklands (incomplete list): Glen Canyon National Recreation Area Grand Staircase–Escalante National Monument Zion National Park Canyonlands National Park Capitol Reef National Park Arches National Park Dinosaur National Monument Navajo National Monument Colorado National Monument Red Rock Canyon National Conservation Area Pink coral sand dunes, Kanab, Utah Vertebrate paleofauna Ornithodires Indeterminate theropod remains geographically located in Arizona, USA. Theropod tracks are geographically located in Arizona, Colorado, and Utah, USA. Ornithischian tracks located in Arizona, USA. Iron oxide concretions The Navajo Sandstone is also well known among rockhounds for its