LOCATION ZORRA TXEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, carbonatic, hyperthermic Lithic Petrocalcic Calciustolls
TYPICAL PEDON: Zorra cobbly loam--rangeland.
(Colors are for dry soil unless otherwise stated.)
A1--0 to 8 inches; dark grayish brown (10YR 4/2) cobbly loam,
very dark brown (10YR 3/2) moist; moderate fine granular
structure; slightly hard, friable; common fine roots; many
fragments of limestone and caliche increasing in amount with depth
and comprise 60 percent by volume, about half of which are less
than 3 inches in diameter; the fragments of limestone are coated
with calcium carbonate and have pendants on the bottom; few
fragments of limestone up to 10 inches along the long axis;
calcareous; moderately alkaline; abrupt wavy boundary. (4 to 20
inches thick)
Ccam--8 to 12 inches; indurate white (10YR 8/2) caliche, that
has a hardness of about 3 on Moh's scale and is laminar in the
upper 1/2 inch; abrupt wavy boundary. (1 to 6 inches thick)
R & Cca--12 to 15 inches; fractured indurated limestone;
cracks and crevices are filled and partially sealed with secondary
calcium carbonate; gradual wavy boundary. (0 to 12 inches thick)
R--15 to 20 inches; fractured limestone bedrock; few seams of
secondary calcium carbonate in upper part.
TYPE LOCATION: Val Verde County, Texas; 7.5 miles west on US
Highway 90 from its junction with US Highway 277 about 5 miles
north of Del Rio; 0.5 mile north on Diablo East Marina road; 0.3
mile east on unpaved National Park Service road; 150 feet north in
rangeland.
RANGE IN CHARACTERISTICS: Solum thickness is 4 to 19 inches and
corresponds to the depth to the petrocalcic horizon. Depth to
limestone bedrock is 5 to 20 inches. Coarse fragments of
limestone and caliche comprise 35 to 80 percent by volume of the
soil mass. About 5 to 50 percent are gravel size, 10 to 35
percent cobble size, and 1 to 60 percent stone size. More than 40
percent of the soil mass less than 20 mm is made up of limestone
fragments and reprecipitated carbonates.
The A horizon is brown (7.5YR 5/2, 4/2; 10YR 5/3, 4/3), dark
grayish brown (10YR 4/2), very dark grayish brown (10YR 3/2), very
dark gray (10YR 3/1), or dark brown (7.5YR 3/2). Moist values and
chromas are 2 or 3. The fine earth fraction is loam, silt loam,
or clay loam with a clay content of 18 to 32 percent. Structure
is weak to moderate, granular to subangular blocky, in fine to
medium sizes. Moist consistence is very friable to friable.
calcium carbonate equivalent is 10 to 30 percent in the fine earth
fraction.
The Ccam horizon is strongly cemented to indurated and laminar in
the upper part with cementation decreasing with depth.
The R & Ca layer is lacking in some pedons. The R layer in most
pedons consists of thick beds of indurated limestone, but some
pedons are over interbedded limestone containing thin strata of
chalk and marl.
Competing Series: These include the Amistad, Boracho, Ector,
Jimenez, Kavett, Olmos, Talpa and Tarrant series. Amistad,
Boracho, Ector, Kavett, Talpa and Tarrant soils have mean annual
soil temperatures less than 72 degrees F. In addition, Amistad
soils are over flaggy limestone. Boracho soils have mixed
mineralogy. Ector, Talpa, and Tarrant soils lack petrocalcic
horizons. Jimenez and Olmos series lack the indurated limestone
layer immediately below the petrocalcic horizon; and in addition,
Jimenez soils have mixed mineralogy and contain many siliceous
pebbles in the soil mass.
GEOGRAPHIC SETTING: Zorra soils are on gently undulating to hilly
uplands. Slopes range from less than 1 to 15 percent. Rock
outcrops are common, especially where gradients are over 8
percent. Stones generally occupy 1 to 15 percent of the surface.
The underlying rock is indurated limestone of the Cretaceous
system, mainly of the Buda and Georgetown formations. Some areas
are interbedded with thin strata of marl or chalk. The mean
annual temperature is 70 degrees to 75 degrees F. Average annual
precipitation ranges from 15 to 23 inches and the Thornthwaite P-E
index ranges from 19 to 31.
GEOGRAPHICALLY ASSOCIATED SOILS: These include the competing
Amistad, Ector, Jimenez, Kavett and Olmos series, as well as the
Dev, Elindio, Felipe, Lozier and Valverde series. Dev and Elindio
soils are over 20 inches deep and occur at lower elevation in
alluvial sediments. Lozier soils occur in similar positions and
lack mollic epipedons and petrocalcic horizons. Valverde soils
occur in similar positions and are over 20 inches deep, and lack
mollic epiedons. Felipe soils are formed over shaly clay and
occur on the steeper slopes and breaks at lower or higher
elevations.
Drainage and Permeability: Well drained; medium to rapid runoff;
moderate perameability.
USE AND VEGETATION: Used entirely for rangeland. Native
vegetation is short and mid-grasses with some desertic shrubs.
Grasses are mainly gramas, tridens or threeawns. Woody plants are
mainly blackbrush, agarito, condalias, pricklypear, guayacan, and
guajillo.
DISTRIBUTION AND EXTENT: Mainly in the southwestern part of the
Edwards Plateau and probably considerable acreage in Mexico. The
series is of moderate extent.
SERIES ESTABLISHED: Val Verde County, Texas; 1979.
REMARKS: The classification of these soils is tentative; a new
subgroup, Lithic Petrocolcic Calciustolls will be proposed. These
soils were formerly included as part of the Ector series and were
formerly classified as Lithosols.