Established Series


The Navaca series consists of deep, moderately well drained, very slowly permeable soils that formed in calcareous clayey and loamy alluvial sediments. Slopes are mainly less than one percent, but range up to 2 percent.

TAXONOMIC CLASS: Clayey over loamy, smectitic, thermic Udertic Haplustolls

TYPICAL PEDON: Navaca clay, frequently flooded - rangeland.
(Colors are for dry soil unless otherwise stated.)

A1--0 to 16 inches; very dark gray (10YR 3/1) clay; black (10YR 2/1) moist; weak coarse blocky structure parting to moderate medium blocky; very hard, very firm; common fine, medium, and coarse roots; few pressure faces on surfaces of peds; calcareous, moderately alkaline; clear wavy boundary.

A2--16 to 31 inches; dark gray (10YR 4/1) clay; very dark gray (10YR 3/1) moist; weak coarse prismatic structure parting to moderate medium blocky; very hard, very firm; common fine, medium, and coarse roots; common pressure faces; calcareous, moderately alkaline; clear wavy boundary. (Combined A horizons 24 to 36 inches thick.)

2C--31 to 45 inches; brown (10YR 5/3) fine sandy loam; dark grayish brown (10YR 4/2) moist; structureless; slightly hard, very friable; few fine roots; calcareous, moderately alkaline; clear smooth boundary.

3C--45 to 80 inches; light yellowish brown (10YR 6/4) loamy fine sand; brown (10YR 5/3) moist; structureless; soft, very friable; calcareous, moderately alkaline.

TYPE LOCATION: Lavaca County, Texas; from the intersection of U. S. Highway 77 North and U. S. Highway 90A in Hallettsville, 2 blocks west on U. S. Highway 90A; 7.8 miles south on county road known locally as Poorfarm Road; 150 feet east in floodplain on the north side of Rocky Creek.

RANGE IN CHARACTERISTICS: Solum thickness to a contrasting loamy horizon ranges from 24 to 36 inches. The upper part of the 10- to 40-inch control section is clayey with clay content ranging from 38 to 60 percent, and COLE values of .07 to .12. The lower part of the control section is loamy with 25 to 35 percent less clay than the upper part. Reaction is typically mildly alkaline or moderately alkaline and calcareous throughout, but some pedons range to neutral below a depth of 50 inches.

The A horizon has hue of 10YR, value of 3 or 4, and chroma of 1. Texture is clay or silty clay and clay loam in lower part. Some pedons have a brownish clay loam surface overwash less than 10 inches thick.

The 2C and 3C horizon has hue of 10YR, value of 5 or 6, and chroma of 2 to 4. Texture is fine sandy loam, sandy clay loam, or loam. Most pedons have a 3C with textures of loamy fine sand or fine sand below a depth of 40 inches.

COMPETING SERIES: There are no competing series in the same family. Similar competing soils include the Cameron, Navidad, Seagoville, Tinn, and Trinity series. All of these lack contrasting textures in the control section except the Cameron and Seagoville soils. Cameron soils have mixed mineralogy and mean annual soil temperatures greater than 72 degrees F. Seagoville soils are Vertisols and have colors with chroma of 2 in the upper part.

GEOGRAPHIC SETTING: Navaca soils are on nearly level floodplains. Slopes are mainly less than 1 percent, but range to 2 percent. The soil formed in calcareous clayey and loamy alluvium. Mean annual precipitation ranges from 32 to 42 inches. Mean annual temperature is 68 to 70 degrees F., and Thornthwaite annual P-E index ranges from 48 to 58.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bleiblerville, Branyon, Frelsburg and Kuy series. Bleiblerville, Branyon, and Frelsburg soils are clayey throughout and are above on upland positions. Kuy soils have thick sandy epipedons and are on terraces slightly above Navaca soils.

DRAINAGE AND PERMEABILITY: Navaca soils are moderately well drained. Permeability is very slow and runoff is slow. Flooding is common in most areas.

USE AND VEGETATION: Navaca soils are used predominantly for rangeland and pasture. Native vegetation is mainly hackberry, elm, oak, and pecan trees and various species of paspalum, panicum, and uniola. Pasture grasses are mainly improved species of bermudagrass. A few areas are in cultivation, mainly to corn and hybrid forage sorghums.

DISTRIBUTION AND EXTENT: Mainly the floodplains of the Lavaca and Navidad rivers and their larger tributary creeks in south central Texas. The series is of moderate extent.


SERIES ESTABLISHED: Lavaca County, Texas; 1986.

REMARKS: Navaca soils were formerly included mainly with the Trinity series.

Diagnostic horizons and features recognized in this pedon are:

Mollic epipedon - 0 to 31 inches.

Vertic feature - 0 to 31 inches evident pressure faces.

Strongly contrasting particle-size class boundary at 31 inches.

National Cooperative Soil Survey
U. S. A.