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Cross Timbers

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NameColor on MapEPA Code‡
Northern Cross Timbers29a
Eastern Cross Timbers29b
Western Cross Timbers29c
Grand Prairie29d
Limestone Cut Plain29e
Carbonate Cross Timbers29f
Arbuckle Uplift29g
Northwestern Cross Timbers29h
Arbuckle Mountains29i

† Status: ✓ = Complete ○ = Needs Image … = Incomplete ∅ = Stub Only

This code refers to the US EPA's Level 4 ecoregion codes for the continental U.S., see here.


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About the Cross Timbers

The Cross Timbers are an irregularly-shaped region extending from north-Central Texas through central Oklahoma and slightly into southeastern Kansas. This region is transitional between more forested regions to the east and formerly grassland-dominated, now grain-growing regions to the west.

The climate here is towards the dry end of a humid subtropical climate; the continental location leaves this region subject to large temperature swings, and sometimes prolonged periods of hotter, colder, wetter, or drier weather. Precipitation is moderately seasonal, with a wet season peaking in May followed by drier summers, slightly wetter fall, and a dry winter. Between 35-40% of the annual precipitation falls from April and June. Relative to areas farther south, there is a bigger difference between spring and fall precpiptation here.

The terrain varies from rolling plains, to hills, ridges and cuestas. A mix of both intermittent and perennial streams of low to moderate gradient are found throughout, and there are some artificial reservoirs. The region is underlain by a mix of different sedimentary rocks, including sandstone, mudstone, claystone, and limestone. Surface soils vary considerably, based both on the underlying rock types, and the topography and type of vegetation cover the soil developed under. Soil pH varies considerably on the different substrates as well as by topography. Much of this region has some of the most acidic soils of any region this far west, with the pH averaging as low as 6 and lower in places. The south of this region however has more limestone and higher pH soils. The soils here are intermediate in suitability for agriculture.

The vegetation is transitional between forests and grassland. Grasslands tend to be dominated by little bluestem (Schizachyrium scoparium), and the dominant trees are the drought-tolerant blackjack oak (Quercus marilandica) and post oak (Quercus stellata). Other important herbaceous plants here include big bluestem (Andropogon gerardii), yellow indiangrass (Sorghastrum nutans), switchgrass (Panicum virgatum), greenbriar (Smilax sp.), and Virginia creeper (Parthenocissus quinquefolia). Other important trees include elm (Ulmus sp.), black hickory (Carya texana). Historically, this region would have experienced regular wildfire, usually severe enough to kill most shrubs but leaving grasses and some of the more fire-tolerant crown trees intact. Due to fire suppression, a dense woody understory has developed in much of this region.

Land use here is a mosaic of different uses. The bulk of the land is a mix of rangeland and pastureland, but there are some areas of wild woodland not used for ranching. There is significant oil extraction here. There is only a small amount of cropland, but it is diversified, and the region produces peanuts, grain sorghum, small grains, hay, cotton, and peaches. This region ranges from heavily populated in places to sparsely in others. Fort Worth is the largest city here, and is completely contained in the region, and its eastern suburb Arlington straddles the eastern border of the region, with about half of its city limits located here. Tulsa is located just outside the region to the east, and Oklahoma City just outside it to the West; both of these metro areas have some suburbs located here, with a greater portion of Oklahoma City's metro area located here. After these, Shawnee, OK is the largest city located here, and the slightyl larger city of Bartlesville, OK also straddles the eastern border of this region. The rest of the region has scattered smaller towns throughout.

Because of the long north-south distance of this region, it borders many different regions to the east. In the south of this region, it is bordered to the east by the Texas Blackland Prairies, a low, flat area with fertile, fine-textured clay soils. North of that there is a small border to the east with the East Central Texas Plains, and north of that, another small border to the east with the South Central Plains (Piney Woods). North of that there is a border to the east and southeast with the Arkansas Valley. The rest of this region, to the north, is bordered to the east by the Central Irregular Plains.

Most of this region is bordered to the west by the Central Great Plains, except in the far north where there is a small border to the west with the Flint Hills. At the south end of this region, there is a relatively broad border to the south with the Edwards Plateau.

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