LOCATION KNOB HILL               NV+CA

Established Series
Rev. ELS/LNL/RLB
09/2015

KNOB HILL SERIES

The Knob Hill series consists of very deep, somewhat excessively drained soils that formed in alluvium from mixed rock sources. The Knob Hill soils are on erosional fan remnants, inset fans, alluvial fans, and relict sand sheets. Slopes are 0 to 8 percent. The mean annual precipitation is about 5 inches and the mean annual temperature is about 65 degrees F.

TAXONOMIC CLASS: Sandy, mixed, thermic Typic Haplocalcids

TYPICAL PEDON: Knob Hill loamy sand-desert wildlife habitat. (Colors are for dry soil unless otherwise noted.) About 20 percent of the soil surface is covered with scattered pebbles.

A--0 to 7 inches; light brown (7.5YR 6/4) loamy sand, brown (7.5YR 4/2) moist; weak thick platy structure; soft, very friable, nonsticky and nonplastic; few fine roots; many very fine interstitial pores; slightly effervescent; moderately alkaline (pH 8.3); clear, smooth boundary. (2 to 18 inches thick)

Bw--7 to 23 inches; light brown (7.5YR 6/4) stratified gravelly loamy sand and very gravelly loamy sand, brown (7.5YR 4/2) moist; massive; soft, very friable, nonsticky and nonplastic; few very fine roots; many very fine and fine interstitial pores; 20 percent pebbles; slightly effervescent; moderately alkaline (pH 8.3); clear, wavy boundary. (12 to 20 inches thick)

Bk1--23 to 37 inches; pinkish gray (7.5YR 7/2) gravelly fine sandy loam, brown (7.5YR 5/2) moist; massive; slightly hard, friable, nonsticky and slightly plastic; many very fine interstitial pores; 20 percent lime-coated pebbles; weakly lime-cemented; 8 percent medium hard white lime concretions; violently effervescent; moderately alkaline (pH 8.2); clear wavy boundary. (10 to 30 inches thick)

Bk2--37 to 60 inches; light brown (7.5YR 6/4) loamy fine sand, brown (7.5YR 5/2) moist; massive; soft, very friable, nonsticky and nonplastic; many very fine interstitial pores; 10 percent lime-coated pebbles; strongly effervescent; moderately alkaline (pH 8.2).

TYPE LOCATION: Clark County, Nevada; at the northwest corner of section 33, T. 23 S., R. 64 E.

RANGE IN CHARACTERISTICS:

Soil moisture: Usually dry. Moist for short periods throughout the moisture control section December through March. Moist periodically in upper part of moisture control section, 10 to 20 days cumulative, June through September.

Soil temperature - 63 to 70 degrees F.

Depth to calcic horizon - 16 to 24 inches

Reaction: Moderately or strongly alkaline



Control section - Clay Content: 8 to 10 percent average.

Rock fragments: Averages 20 to 35 percent, mostly pebbles.



A horizon - Hue 7.5YR or 10YR

Chroma: 2 through 4



Bw horizon Hue: 7.5YR or 10YR.

Value: 6 or 7 dry, 4 or 5 moist.

Chroma: 2 through 4.

Texture: Gravelly loamy sand, stratified loamy sand and gravelly sandy loam.

Rock fragment: 20 to 25 percent.



Bk1 horizons Hue: 7.5YR or 10YR

Value: 7 or 8 dry, 5 or 6 moist.

Chroma: 1 through 3.

Texture: Gravelly fine sandy loam,, stratified loamy sand and gravelly sandy loam.

Consistence: Slightly hard or hard, friable or firm.

Reaction: Moderately alkaline or strongly alkaline.

Other features: Many thick lime coats ranging from undersides to completely coating rock fragment; 8 percent weakly lime cemented concretions.



Bk2 horizon - Hue: 7.5YR or 10YR.

Value: 6 or 7 dry.

Chroma: 2 through 4.

Texture: Loamy fine sand to very gravelly loamy sand.

Rock fragment: 10 to 40 percent.

Other features: Few to many thick lime coats on vertical and undersides of rock fragments.

COMPETING SERIES: These are the Arada(NV) and Lovelace(CA) series. Arada soils are deeper than 24 inches to the calcic horizon and contain less than 15 percent gravel in the upper portion of the control section. Lovelace soils contain less than 15 percent coarse fragment in the control section and lack appreciable summer precipitation.

GEOGRAPHIC SETTING: Knob Hill soils are on erosional fan remnants, inset fans, alluvial fans and relict sand sheets. These soils formed in alluvium from mixed rock sources. Slopes are 0 to 8 percent. Elevations are 1,400 to 3,500 feet. The climate is arid with hot dry summers and mild winters. The mean annual precipitation is 4 to 9 inches; mean annual temperature is 60 to 68 degrees F., and the frost-free season is 180 to 250 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Arizo, Aztec, Bluepoint, Caliza, and Pittman soils. Arizo, Aztec, and Bluepoint soils lack calcic horizons. Arizo, Caliza, and Pittman soils have skeletal control sections, and in addition, Pittman soils have a petrocalcic horizon at a depth between 20 and 40 inches.

DRAINAGE AND PERMEABILITY: Somewhat excessively drained; slow or medium runoff; moderately rapid permeability.

USE AND VEGETATION: Rangeland and wildlife habitat. The present vegetation is mainly creosotebush, white bursage, Indian ricegrass, sand dropseed, and big galleta.

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

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

SERIES ESTABLISHED: Clark County (Las Vegas and El Dorado Valleys Area), Nevada. 1964.

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

Ochric epipedon - The zone from 0 to 7 inches (A horizon)

Particle size control section - The zone from 10 to 40 inches. (Bk1, Bk2 and part of the Bk3 horizon)

Calcic horizon - The zone beginning at 23 inches

Responsibility for this series was transferred from Davis to Phoenix 9/2015. The last revision to the series was 5/1997. ET

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National Cooperative Soil Survey
U.S.A.