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Crowley's Ridge (alsoCrowleys Ridge) is a geological formation that rises 250 to 550 feet (170 m) above thealluvial plain of theMississippi embayment in a 150-mile (240 km) line from southeasternMissouri to theMississippi River nearHelena, Arkansas. Named for settlerBenjamin Crowley,[1] it is the most prominent feature in theMississippi Alluvial Plain betweenCape Girardeau, Missouri, and theGulf of Mexico.
The narrow rolling hill region rising above the flat plain is the sixth, and smallest, natural division of the state ofArkansas. The southern part is protected withinOzark–St. Francis National Forest.
Most of the major cities of theArkansas Delta region lie along Crowley's Ridge. It was named afterBenjamin Crowley, known as the first American settler to reach the area, sometime around 1820. TheCivil WarBattle of Chalk Bluff was fought on Crowley's Ridge on May 1–2, 1863.
The ridge is primarily composed of the windblown glacially derived sediment known asloess. It contrasts greatly with the flat table land around it and with the black soil that makes up the delta. The ridge varies from half a mile to 12 miles (19 km) wide and reaches an elevation of 550 feet (170 m) near its northern extremity. The highest point on the ridge in Arkansas is "Legacy Mountain" at the Craighead County solid waste site south of Jonesboro.
Prevailing winds blow dust into the river fogs. The fog wetted dust tends to fall and make loess deposits on the downwind sides of rivers, such as the east and north sides of the Mississippi River, as well as the east side of the Black River.[2] These loess deposits are a classic example of periglacialloess.[3][4] Crowley's Ridge is a natural loess accumulation point. A comparable example of this type of deposit is theLoess Hills in northwestern Missouri and western Iowa.
At one time, the ridge was thought to have been an island between theMississippi River andOhio River that was isolated as a long low hilly ridge after the rivers changed course millions of years ago.[5] Recent seismic evidence, however, questions the fluvial origin by focusing on uplift along ridge bounding faults.[6]
There is evidence that the area's elevation has increased over the years, suggesting that uplift is still taking place. This alternative explanation posits a link between the ridge and the nearbyNew Madrid Seismic Zone.[6]
The flora and fauna of the ridge seem more closely related to theKentucky andTennessee hills to the east than to theOzark Mountains to the west. This unique habitat has been protected by the establishment of several state and city parks, theSt. Francis National Forest, recreational lakes, and in 1997 anational scenic byway, theCrowley's Ridge Parkway.[7][8]
The soils in this area are moderately fertile and sometimes rich. The land is moderately rugged, discouraging row-crop agriculture. These soils are easily eroded. There is some commercial agriculture in theloessal plains area of the ridge. The ridge is surrounded by the fertile lands of thedelta region. The vegetation is predominantlyoak andhickory forests, similar to vegetation found in theAppalachian Mountains. Examples are thetulip tree (or yellow poplar) and theAmerican beech. Ferns and flowers abound here, including theAmerican bellflower,fire pink,butterfly weed,cardinal flower,blue lobelia,phlox,verbena,wild hydrangea,hibiscus,aster, andyellow jasmine. The low-lying areas around the ridge were once muchswampier, and the ridge provided a natural and more healthful place for settlers to establish homes. The ridge became a natural north-south communications link for the region, since travel along the ridge was much easier than through the swampy lowlands.[9]
The region adjacent to the ridge is covered with thick deltaic soils, and fewfossils are found except in gravel pits. These pits sometimes reveal the teeth of large mastodons, mammoths and horses, which roamed the continent as recently as 10,000 years ago. Crowley's Ridge contains important exposures of fossiliferous Tertiary sediments and contains the only documentedMiocene exposures in the state. Asilicified conifer stump weighing several tons was unearthed near Wittsburg, and many more were found aroundPiggott.Mastodon bones were found within the city limits ofHelena at the southern end of the ridge. NearForrest City, in the bed of Crow Creek, a deposit ofoyster shells estimated to be nearly 7,000,000 cubic yards in size was discovered.[9]
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36°08′31″N90°34′30″W / 36.142°N 90.575°W /36.142; -90.575
