No major metropolitan areas lie wholly within the Cross Timbers, although roughly the western half of the Dallas-Fort Worth Metroplex does, including the cities of Fort Worth, Denton, Arlington, and Weatherford.[3] The western suburbs of the Tulsa metropolitan area and the northeastern suburbs of the Oklahoma City metropolitan area also lie within this area.[2] The main highways that cross the region are I-35 and I-35W going north to south (although they tend to skirt the Cross Timbers' eastern fringe south of Fort Worth) and I-40 going east to west. Numerous U.S. Highways also cross the area.[2][3] I-35 means a portion of Austin and Travis County is also included in the Cross Timbers.[1]
The woodland and savanna portions of the Cross Timbers are mainly post oak and blackjack oak on coarse, sandy soils;[4]fire suppression in recent years has increased forest density and allowed eastern redcedar to invade as well. The short, stout oaks that grow in the Cross Timbers were not usable as timber, and those that were not cleared for farmland constitute one of the least disturbed forest types in the eastern United States, with some 890,000 acres (3,600km2) of old-growth forest scattered throughout the region.[5] These old-growth forests contain millions of post oak from 200 to 400 years old and red cedar over 500 years old.[5] The prairie portions are chiefly tallgrass on finer, dry soils.[2] Overall, the Cross Timbers are not as arable as the surrounding ecoregions.[3] Today, land use is a mixture of rangeland, pastures, and farmland.[2] The area has also been an important site of oil extraction for over 80 years.[3]
Geologically speaking, the Cross Timbers are underlain by Pennsylvanian and Cretaceous-era sandstone and limestone that has been moderately dissected, giving the region a gently to moderately rolling topography,[3][4] including some cuestas.[2] Although local relief is relatively low, it is generally greater than that in the surrounding ecoregions, although this is not the case with the Flint Hills in Kansas.[4]
Ecologically, the EPA includes the Cross Timbers as part of the vast Great Plains, which comprise Level I Ecoregion 9.0, stretching from central Alberta in Canada to northern Mexico.[6] More specifically, the Cross Timbers fall into Level II Ecoregion 9.4, the smaller South Central Semi-Arid Plains.[7] In southern Oklahoma, the Cross Timbers are located on the very edge of the Great Plains, as they border directly parts of Level I Ecoregion 8.0, the Eastern Temperate Forests; elsewhere, the Cross Timbers are separated slightly from the Eastern Temperate Forests.[2] In turn, the Cross Timbers are themselves subdivided into nine Level IV Ecoregions:
Coal mining has historically been an important activity, as bituminous coal deposits are found throughout the region;[13] indeed, the town of Newcastle in Young County was named after the English city of the same name due to the coal connection.[14]
In the mid-to-late 19th century, ComancheIndians occupied this area, and it became a flash point for conflict between various groups of white settlers, the Comanche, and the U.S. Cavalry; FortsBelknap and Richardson were built in the area to protect this part of the frontier.[15]
A broader, southern extension of the Grand Prairie, found only in Texas; it is underlain by limestone rather than sandstone, and serves as a physiological and vegetational transition to the Edwards Plateau, which it borders to the south. All of Hamilton and Coryell counties, large parts of Bell, Lampasas, Mills, Erath, and Bosque counties, and smaller parts of Williamson, Burnet, Brown, Comanche, Hood, Somervell, and McLennan counties, including the towns of Killeen, Copperas Cove, and Lampasas as well as the Fort CavazosArmy base, fall within this region.[8] Among the few major roads that cross the Limestone Cut Plains are US 281 north to south and US 84 east to west.
29f: Carbonate Cross Timbers
This ecoregion exists as an enclave within the Western Cross Timbers, stretching from southern Jack County, Texas across northwestern Palo Pinto County into eastern Stephens County, as well as tiny parts of Young and Eastland counties. The region features a limestone substrate as opposed to sandstone, and has greater topographical relief and denser and different vegetation than other parts of the Cross Timbers. No towns of any size lie within this area, although Possum Kingdom Lake and State Park do;[8] the region is crossed by US 180 and Texas State Highway 16.
29g: Arbuckle Uplift
Covering a fairly small area in south-central Oklahoma and underlain by a unique mosaic of several different minerals, this region includes the town of Ardmore.[2]
29h: Northwestern Cross Timbers
An extension in two branches of the Cross Timbers into southwestern Oklahoma, this area features reduced tree density and height, but also small forests dominated by sugar maple, bur oak, and live oak in deeper river canyons. The towns of Duncan, Oklahoma and Walters, Oklahoma, lie in this region.[2]
29i: Arbuckle Mountains
The Arbuckle Mountains are located in a small area nestled in between regions 29g and h; it is made of folded, rather than dissected, limestone, sandstone, and dolomite, and features the greatest topographical relief of the entire Cross Timbers, though not the highest elevations. The landscape includes many caves, sinkholes, springs, and streams.[2]I-35 crosses this region north to south.
Climatology
Part of the difference in the Cross Timbers region and the surrounding regions west (drier) and east (wetter) has to do with the dry line which separates humid air from the Gulf of Mexico from the dry air of the Llano Estacado, the Texas Panhandle, and the High Plains.
History
The thick growth formed an almost impenetrable barrier for early American explorers and travelers. Washington Irving, in 1835, described it as "like struggling through forests of cast iron."[16]Rachel Plummer, while a captive of the Comanche in 1836, described it as "a range of timber-land from the waters of Arkansas, bearing a southwest direction, crossing the False Ouachita, Red River, the heads of Sabine, Angelina, Natchitoches, Trinity, Brazos, Colorado...the range of timber is of an irregular width, say 5 to 35 miles wide...abounding with small prairies, skirted with timber of various kinds — oak, of every description, ash, elm, hickory, walnut and mulberry...the purest atmosphere I ever breathed was that of these regions."[17]Josiah Gregg described the Cross Timbers in 1845 as varying in width from five to thirty miles and attributed their denseness to the continual burning of the prairies.[18]
The Cross Timbers vary in width from five to thirty miles, and entirely cut off the communication betwixt the interior prairies and those of the great plains. They may be considered as the "fringe" of the great prairies, being a continuous brushy strip, composed of various kinds of undergrowth; such as black-jack, post-oaks, and in some places hickory, elm, etc., intermixed with a very diminutive dwarf oak, called by the hunters, "shin-oak." Most of the timber appears to be kept small by the continual inroads of the "burning prairies;" for, being killed almost annually, it is constantly replaced by scions of undergrowth; so that it becomes more and more dense every reproduction. In some places, however, the oaks are of considerable size, and able to withstand the conflagrations. The Underwood is so matted in many places with grapevines, green-briars, etc., as to form almost impenetrable "roughs," which serve as hiding-places for wild beasts, as well as wild Indians; and would, in savage warfare, prove almost as formidable as the hammocks of Florida.
—Josiah Gregg
Robert Neighbors and Rip Ford reached the "Cross Timbers, two parallel strips of timber region that ran down the middle of Texas", in 1849 while blazing an emigrant trail from Austin to El Paso.[19]:116
Anderson, Roger C., James S Fralish, Jerry M. Baskin (eds.). Savannas, Barrens, and Rock Outcrop Plant Communities of North America. Cambridge University Press, 1999. ISBN0-521-57322-X
Francaviglia, Richard V. The Cast Iron Forest: A Natural and Cultural History of the North American Cross Timbers. University of Texas Press, 2000. ISBN0-292-72515-9
Dale, Edward Everett. The Cross Timbers: Memories of a North Texas Boyhood. Austin, TX: University of Texas Press, 1966. ISBN0-292-73611-8
Roach, Joyce. Wild Rose: A Folk History of a Cross Timbers Settlement, Keller, Texas. Denton, TX: University of North Texas Press, 1996. ISBN0-89865-972-8
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https://www.epa.gov/eco-research/ecoregion-download-files-state-region-6#pane-41 Under "Texas." 4 maps contain additional information on Cross Timbers, such as which plants grow in the level IV ecoregions. The maps have county borders but no names; however, they detail rivers, lakes, and major cities, and contain photographs. There is also a Texas ecoregion report PDF which describes Cross Timbers vegetation and other features in much more detail than the maps. Under "Oklahoma," there is no ecoregion report PDF yet but more details are contained in the 4 PDF maps.
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