cuesta

cuesta, asymmetric ridge characterized by a short, steep escarpment on one side, and a long, gentle slope on the other. The steep side exposes the edge of erosion-resistant rock layers that form the cuestas. They are usually formed by erosion in plains areas underlain by gently dipping sedimentary rock layers. Cuestas have a more gentle dip than similar structures called hogbacks. Along the U.S. Atlantic and Gulf coastal plains are found a series of low subdued cuestas composed of seaward-dipping and poorly cemented Cretaceous and Tertiary sandstones, while the intervening lowlands are underlain by impermeable clays. These conditions produce ideal structures for artesian water supply systems, which have been extensively tapped by coastal cities. A well-known example of a cuesta is the Niagara cuesta that runs westward across W New York State and Ontario, then swings northward, forming the peninsula between Lake Huron and Georgian Bay, and finally curves southward, forming the Door Peninsula between Green Bay and Lake Michigan. Following withdrawal of the last Pleistocene ice sheet about 10,000 years ago, Niagara Falls first formed where the Niagara River crosses the Niagara cuesta at Lewiston, N.Y., and Queenston, Ont. Since then, the falls have migrated nearly 7 mi (11 km) southward as a result of undercutting and rockfall, leaving the steep-walled Niagara Gorge to mark its path.

In structural geology and geomorphology, a cuesta (from Spanish: "slope") is a ridge formed by gently tilted sedimentary rock strata in a homoclinal structure. Cuestas have a steep slope, where the rock layers are exposed on their edges, called an escarpment or, if more steep, a cliff. Usually an erosion-resistant rock layer also has a more gentle slope on the other side of the ridge called a 'dip slope'.

Two well-known cuestas in western New York and southern Ontario are the Onondaga escarpment and the Niagara escarpment. The dip of the Onondaga is about 40 feet per mile (about 7.6 m/km) to the south. The escarpment edge faces north and, in its most populated section, runs roughly parallel to the southern Lake Ontario shoreline.

Most Coastal Plains around the world are punctuated by a series of cuestas that parallel the coast. The cuestas have gentle slopes over resistant strata at the surface and steeper slopes where these resistant strata are cut. That means that steeper slopes face inside anticlinals and outside eroded sinclinals. The Reynosa Plateau is the most coast-ward cuesta, which sees surface expression with the Bordes-Oakville escarpment, on the northwest side and a low ridge on the eastern boundary, called the Reynosa cuesta, where the deposits dip below later Pliocene-Pleistocene deposits of the Willis and Lissie Formation.

Cuestas have less dramatic expression in the United Kingdom, with two notable examples being the northwest-facing escarpment of the Jurassic chalk White Horse Hills and the similarly-aligned escarpment of the Cotswolds, sometimes called the Cotswold Edge. In continental Europe, the Swabian Alb offers particularly good views of cuestas in Jurassic rock. In France, the term for a cuesta is the same as for a coastline: "côte". Notable French cuestas are the wine-growing regions of Côte d'Or and Côtes du Rhône.

References

See also

• Escarpment
• Dip slope
• Strike and dip
• Hogback

External links

• Escarpment geology