Petrified Forest National Park in the context of "Petrifaction"

Petrified wood (from Ancient Greek πέτρα meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of fossilized wood, the fossilized remains of terrestrial vegetation. Petrifaction is the result of a tree or tree-like plants having been replaced by stone via a mineralization process that often includes permineralization and replacement. The organic materials making up cell walls have been replicated with minerals (mostly silica in the form of opal, chalcedony, or quartz). In some instances, the original structure of the stem tissue may be partially retained. Unlike other plant fossils, which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material.

The petrifaction process occurs underground, when wood becomes buried in water or volcanic ash. The presence of water reduces the availability of oxygen which inhibits aerobic decomposition by bacteria and fungi. Mineral-laden water flowing through the sediments may lead to permineralization, which occurs when minerals precipitate out of solution filling the interiors of cells and other empty spaces. During replacement, the plant's cell walls act as a template for mineralization. There needs to be a balance between the decay of cellulose and lignin and mineral templating for cellular detail to be preserved with fidelity. Most of the organic matter often decomposes, however some of the lignin may remain. Silica in the form of opal-A, can encrust and permeate wood relatively quickly in hot spring environments. However, petrified wood is most commonly associated with trees that were buried in fine grained sediments of deltas and floodplains or volcanic lahars and ash beds. A forest where such material has petrified becomes known as a petrified forest.

A kiva (also estufa) is a space used by Puebloans for rites and political meetings, many of them associated with the kachina belief system. Among the modern Hopi and most other Pueblo peoples, "kiva" means a large room that is circular and underground, and used for spiritual ceremonies and a place of worship.

Similar subterranean rooms are found among ruins in the Southwestern United States, indicating uses by the ancient peoples of the region including the ancestral Puebloans, the Mogollon, and the Hohokam. Those used by the ancient Pueblos of the Pueblo I Period and following, designated by the Pecos Classification system developed by archaeologists, were usually round and evolved from simpler pit-houses. For the Ancestral Puebloans, these rooms are believed to have had a variety of functions, including domestic residence along with social and ceremonial purposes.

This list of North American deserts identifies areas of the continent that receive less than 10 in (250 mm) annual precipitation. The "North American Desert" is also the term for a large U.S. Level 1 ecoregion (EPA) of the North American Cordillera, in the Deserts and xeric shrublands biome (WWF). The continent's deserts are largely between the Rocky Mountains and Sierra Madre Oriental on the east, and the rain shadow–creating Cascades, Sierra Nevada, Transverse, and Peninsular Ranges on the west. The North American xeric region of over 95,751 sq mi (247,990 km) includes three major deserts, numerous smaller deserts, and large non-desert arid regions in the Western United States and in northeastern, central, and northwestern Mexico.