ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...

58 INTRODUCTION/SOIL-RELATED GEOLOGY, PINEYWOODS, POST OAK SAVANNAH
the Queen City are underlain by impermeable clay, seepage bogs can result (e.g., Van Zandt
County—Kral 1955). The Queen City produces a gently rolling topography and occupies a
relatively large surface area in East Texas (Sellards et al. 1932). Soils of the Queen City
Formation are typically Ultisols with a sandy surface layer over a loamy subsoil. To the west
they underlie parts of the Post Oak Savannah, and in the more moist areas to the east they
support extensive portions of the Pineywoods.
REKLAW FORMATION—The Eocene marine-deposited Reklaw Formation consists of a layer of
dark silty shale over a layer of dark gray to green, very fine glauconitic silty sand and contains
some lignite (Sellards et al. 1932; C. Miller Drilling 2001). Soils of the Reklaw Formation are
Ultisols with a loamy surface layer over a reddish clayey subsoil. Though they support some
Post Oak Savannah, the red somewhat clayey (sandy clay) soils derived from the Reklaw are
“less forested” than adjacent areas developed from the Carrizo and Queen City formations.
The Reklaw has sometimes been described as “a red prairie belt between two broad, oakforested
ridges” (Sellards et al. 1932). A second belt of the Reklaw is found on the edge of the
Sabine Uplift and underlies portions of the Pineywoods.
CARRIZO FORMATION—The Eocene Carrizo Formation is composed of continental alluvial
plain sand deposits, is generally grayish yellow in color (weathering light brown), and is
loose, permeable, and friable in nature (McBryde 1933; Kreitler et al. 1980). The surface
outcrop, which occurs entirely within Texas, varies from about three to twelve miles (4.8 to
19.2 km) in width (Sellards et al. 1932; McBryde 1933) and extends in a southwest to northeast
line from the Bexar-Guadalupe County line in the very southwestern portion of East
Texas to Cass County in the extreme northwest. It then trends south to northern Sabine County
(see page 217 for additional discussion) (Sorrie & Weakley 2001). Soils of the Carrizo Formation
are mainly Entisols and Ultisols. Some of these soils are so sandy that a finer-textured subsoil
cannot develop within 2 meters (80 inches) of the surface (they are thus Entisols). Other areas
develop a subsoil layer of slightly finer texture than the thick sandy surface and are classified
as Ultisols (see page 47 for additional discussion). These loose, coarse to fine sandy soils
underlie a significant portion of the Post Oak Savannah (McBryde 1933; MacRoberts et al.
2002b) and small areas of the Pineywoods. The most characteristic vegetation type developed
on the Carrizo Formation is xeric sandylands (MacRoberts et al. 2002b), also known as Dry
Uplands on Deep Coarse Sands (see page 92). This vegetation type is characterized by such
tree species as Quercus incana (bluejack or sandjack oak), Q. margarettiae (sand post oak),
Q. stellata (post oak), and Carya texana (black hickory), as well as a variety of typical herbaceous/understory
species, including Aristida desmantha (curly threeawn), Asimina parviflora
(small-flower pawpaw), Brazoria truncata (rattlesnake flower), Cyperus grayoides
(Mohlenbrock’s sedge), Polanisia erosa (large clammyweed), Selaginella arenicola subsp. riddellii
(Riddell’s spike-moss), and Yucca louisianensis (Louisiana yucca) (MacRoberts et al. 2002b). In
the Pineywoods, Pinus palustris (longleaf pine) can be important in the overstory. Fire and periodic
drought appear to be important factors in maintaining this xeric sandylands community
typically found on the Carrizo Formation (MacRoberts et al. 2002b).
Another interesting type of vegetation that is found in part on the Carrizo Formation is
the disjunct “Lost Pines” area of Bastrop County. This area of pine-oak woodland, somewhat
similar to the xeric sandylands, is unusual in being dominated by loblolly pines isolated
approximately 100 miles (162 km) west of the main body of East Texas pines (Maxwell 1970;
Texas Parks and Wildlife 2002b; Taber & Fleenor 2003). The infiltration of water into the
porous sandy soils of the Carrizo and nearby sandy and gravelly layers (e.g., Quaternary
gravels) has allowed the survival of the pines “which would otherwise not be successful in
this area of Central Texas” (Riskind & Moreland 1973).
The Carrizo sands are an important local center of endemism in the West Gulf Coastal