LOCATION FLATTOP NV
Established Series
Rev. LNL/VDL/ELS
04/2015
FLATTOP SERIES
Flattop soils typically have well developed gravel pavements over light brown and reddish brown clay loam B2t horizons, and unconformable very gravelly B3tca horizons and Cca horizons
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, thermic Typic Natrargids
TYPICAL PEDON: Flattop gravelly clay loam - rangeland (Colors are for dry soil unless otherwise noted.) The soil surface is about 95 percent covered with a well developed gravel pavement of subangular and rounded pebbles ranging from 1/2 to 3 inches in diameter. Few pebbles have a desert varnish on their exposed surfaces.
Bt1--0 to 2 inches; light brown (7.5YR 6/4) gravelly clay loam, brown (7.5YR 4/4) moist; moderate medium prismatic structure; very hard, friable, sticky, plastic; few very fine and fine roots; many very fine and fine vesicular pores; many thin clay films in pores and few thin clay films on faces of peds; violently effervescent; very strongly alkaline (pH 9.0); abrupt smooth boundary. (1 to 4 inches thick)
Bt2--2 to 5 inches; variegated reddish brown (5YR 5/4 and 4/4) light clay loam, reddish brown (5YR 4/4) moist; moderate medium prismatic parting to moderate thin platy structure; slightly hard, friable, sticky, plastic; common very fine and few fine roots- many very fine interstitial, and common very fine tubular pores; many thin clay films in pores, and few moderately thick and thin clay films on faces of peds; violently effervescent; moderately alkaline (pH 8.4); abrupt irregular boundary. (2 to 5 inches thick)
2Btk3--5 to 10 inches; yellowish red (5YR 5/6) gravelly fine sandy loam, yellowish red (5YR 4/6) moist, massive; soft, very friable, nonsticky, slightly plastic; common very fine and few fine roots; many very fine and fine interstitial pores; few very thin clay bridges between sand grains and coating sand grains; common fine and medium distinct pinkish white (7.5YR 8/2) lime and gypsum masses; violently effervescent; strongly alkaline (pH 8.6); clear smooth boundary. (0 to 7 inches thick)
2Btk4--10 to 22 inches; yellowish red (5YR 5/6) very gravelly fine sandy loam, yellowish red (5YR 4/6) moist; massive; soft, very friable, nonsticky, nonplastic; few very fine roots; many very fine and fine interstitial pores; few verv thin clay bridges between sand grains and coating sand grains; common medium distinct pinkish white (7.5YR 8/2) lime and gypsum segregations and lime coatings on pebbles; violently effervescent; moderately alkaline (pH 8.4); gradual smooth boundary. (7 to 15 inches thick)
3Ck1--22 to 30 inches; light brown (7.5YR 6/4) very gravelly loamy fine sand, brown (7.5YR 4/4) moistsingle grained; loose; few very fine roots; many fine and medium interstitial pores pinkish white (7.5YR 8/2) coatings on the undersides of pebbles; violently effervescent; moderately alkaline (pH 8.4); gradual wavy boundary. (6 to 17 inches thick)
3Ck2--30 to 50 inches; stratified, in 1 to 9-inch bands, light reddish brown (5YR 6/4) very gravelly fine sand and pinkish white (7.5YR 8/2) strongly lime-cemented very gravelly material, reddish brown (5YR 5/4) and pinkish gray (7.5YR 6/2) moist; massive; uncemented material is loose and soft, loose and very friable, nonsticky, nonplastic; cemented material is very hard, very firm; common very fine and fine interstitial pores; violently effervescent; moderately alkaline (pH 8.4).
TYPE LOCATION: Clark County, Nevada; approximately 2.3 miles north of U. S. Highway 91 and 600 feet east of Elgin Road; about 700 feet west and 600 feet south of the NE corner of sec. 22, T.13S., R.68E.
Range in Characteristics: Solum thickness is 16 to 25 inches.
Mean annual soil temperature is 60 to 68 F. These soils are usually dry, mainly during the spring, summer and autumn months.
A 1- to 3-inch thick A1 horizon occurs around the base of shrubs. The Al horizon has hue of 7.5YR or 5YR, value of 7 or 6 dry, 5 or 4 moist, chroma of 2 through 4. It has few to many fine and medium vesicular pores.
The B2t horizon has hue of 5YR or 7.5YR, value of 4 through 6 moist and 4 or 5 dry, chroma of 4 through 6. It is dominantly clay loam, but includes sandy clay loam or loam. The average clay content of the argillic horizon is 18 to 30 percent and volume of coarse fragments is 35 to 50 percent. The exchangeable sodium percentage is 15 to 30 percent. Segregated lime occurs in the lower B2t or B3t horizons and fine salt and/or gypsum segregations occur in the B3t or C1 horizons of some pedons.
The solum rests unconformably over very gravelly sandy material containing 50 to 85 percent gravel.
These materials are weakly or strongly lime-cemented below 28 inches in most pedons. Individual cemented strata rarely exceed 14 inches in thickness and are as thin as 1 inch in Some pedons. pH usually ranges from 8.4 to 9.6, but can be as low as 8.0 where sufficient amounts of gypsum are present.
Competing Series and their Differentiae: These are the Casa Grande and Gothard soils which lack contrasting textures within their control sections and have fine-loamy control sections.
Setting: Smooth, gently and moderately sloping alluvial fans at elevations of 1,600 to 2,600 feet. Slope gradients are 2 to 8 percent. The surface is dissected by few shallow and occasional- deep channels. Flattop soils formed in alluvium from mixed sedimentary and metamorphic rocks. The climate is hot and arid with a mean annual temperature of 66 to 70 F., average January temperature of 45 to 47 F., and average July temperature of 82 to 85 F. The mean annual precipitation is 4 to 6 inches.
Principal Associated Soils: These are the Arizo, Crystal Springs, Mormon Mesa, and St. Thomas soils. Arizo soils have sandy-skeletal control sections. Crystal Springs and Mormon Mesa soils have lime-indurated horizons, and lack argillic horizons. St. Thomas soils have bedrock at depths of less than 20 inches.
Use and Vegetation: These soils are used for rangeland during the spring months when annuals abound. The vegetation consists of a very sparse stand of creosotebush, white bursage, cholla, yucca, and annuals.
Distribution and Extent: These soils are of moderate extent in southern Nevada. They may also occur in adjacent southwestern Utah and possibly in southern Arizona.
Series Established: Clark County (Virgin River Area), Nevada, 1969.
Remarks: Flattop soils were formerly classified as Red Desert soils.
OSED scanned by NSSQA. Last revised by state on 9/71. Responsibility for this series was transferred from Davis to Phoenix 4/2015. ET
National Cooperative Soil Survey
U.S.A.