LOCATION BLACKNAT                NV

Established Series
Rev. DJM/ET
04/2015

BLACKNAT SERIES

The Blacknat series consists of very shallow over soft bedrock, excessively drained soils that formed in eolian sand derived mainly from limestone. Blacknat soils are on stream terraces. Slopes are from 2 to 4 percent. The mean annual precipitation is about 5 inches. The mean annual temperature is about 68 degrees F.

TAXONOMIC CLASS: Sandy, mixed, thermic, shallow Typic Petrocalcids

TYPICAL PEDON: Blacknat gravelly fine sand - rangeland. (Colors are for dry soil unless otherwise noted.) The soil surface is covered with 20 percent pebbles.

A1--0 to 1 inch; light brown (7.5YR 6/4) gravelly fine sand, brown (7.5YR 4/4) moist; strong fine platy structure; soft, very friable, nonsticky and nonplastic; few fine roots; many very fine and fine interstitial pores; 20 percent pebbles; 4 percent calcium carbonate equivalent; slightly effervescent; moderately alkaline (pH 8.2); clear smooth boundary. (1 to 3 inches thick)

A2--1 to 7 inches; light brown (7.5YR 6/4) fine sand, brown (7.5YR 4/4) moist; single grained; loose, nonsticky and nonplastic; few fine; many very fine and fine interstitial pores; 5 percent calcium carbonate equivalent; violently effervescent; moderately alkaline (pH 8.2); abrupt smooth boundary. (3 to 7 inches thick)

2Bkm--7 inches; pinkish white (7.5YR 8/2) cemented material, pink (7.5YR 8/3) moist; massive; very rigid; indurated with calcium carbonate; violently effervescent.

TYPE LOCATION: Northeastern Clark County, Nevada; approximately 1.2 miles southwest of the confluence of Halfway Wash and the Virgin River along the west side of the river; 1,850 feet south and 178 feet east of the northwest corner of section 7, T. 15 S., R. 68 E.; USGS Overton N.E., 7.5 minute topographic quadrangle; 36 degrees 38 minutes 49 seconds north latitude and 114 degrees 19 minutes 44 second west longitude, NAD 83; UTM 11s 738783e, 4059045n, NAS-C.

RANGE IN CHARACTERISTICS:

Soil moisture - Usually dry, moist in some part for short periods during winter and early spring and for brief periods between July and October following convection storms; typic aridic moisture regime.

Soil temperature: 65 to 71 degrees F.

Depth to petrocalcic horizon - 5 to 10 inches.

Control section -
Clay content: 2 to 6 percent;
Rock fragments: averages 5 to 10 percent, mainly pebbles. Lithology of fragments is dominantly sedimentary rocks composed of limestone and dolomitic limestone.
Reaction - moderately alkaline or strongly alkaline.


A horizon - Value: 5 or 6 dry, 4 or 5 moist.

Chroma: 4 or 6 dry and moist.

Calcium carbonate equivalent: 1 to 5 percent in the less than 2 millimeter fraction.

2Bkm horizon - Cementation: Very strongly cemented or indurated petrocalcic hardpan.

Other Features: Petrocalcic horizon ranges from 2 to 5 feet thick.

COMPETING SERIES: This is the Tonuco series. Tonuco soils have a calcic horizon and a soil moisture regime typical of the Sonoran desert.

GEOGRAPHIC SETTING: Blacknat soils are on stream terraces. They formed in eolian sand derived mainly from limestone over a petrocalcic horizon. Slopes are from 2 to 4 percent. Elevations range from 1,400 to 2,000 feet. The climate is arid with warm winters and hot, dry summers. The mean annual precipitation is about 5 to 7 inches, mean annual temperature is about 66 to 68 degrees F., and the frost-free period is 180 to 300 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bard and Monger series. Bard soils have a loamy particle size control section and are greater than 10 inches depth to the petrocalcic horizon. Monger soils are deep over soft bedrock.

DRAINAGE AND PERMEABILITY: Exedssively drained; low runoff; rapid permeability; saturated hydraulic conductivity class is high or very high.

USE AND VEGETATION: Rangeland and recreation use. The present vegetation is mainly white bursage, white ratney, creosotebush, Nevada ephedra, and cholla.

DISTRIBUTION AND EXTENT: Southern Nevada. These soils are not extensive. MLRA 30.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: PHOENIX, ARIZONA

SERIES PROPOSED: Clark County, Nevada, 2004. The name is coined.

REMARKS:
Diagnostic horizons and features recognized in this pedon are:

Ochric epipedon - The zone from about 0 to 1 inches. (A horizon)

Petrocalcic horizon - The zone from about 7 to greater than 60 inches. (Bkm horizon)

Particle size control section - The zone from 0 to 7 inches (The A horizons).

Responsibility for this series was transferred from Davis to Phoenix 4/2015. The last revision to the series was 3/2007. ET

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National Cooperative Soil Survey
U.S.A.