LOCATION POCUM                   AZ

Established Series
Rev. AAD/DEW/PDC/WWJ
10/2013

POCUM SERIES

The Pocum series consists of shallow to hardpan, well drained soils that formed in mixed colluvium and alluvium derived from volcanic rocks. Pocum soils are on mesas and have slopes of 1 to 10 percent. The mean annual precipitation is about 12 inches and the mean annual air temperature is about 54 degrees F.

TAXONOMIC CLASS: Loamy, mixed, superactive, mesic, shallow Calcic Petrocalcids

TYPICAL PEDON: Pocum gravelly fine sandy loam - rangeland. (Colors are for dry soil unless otherwise noted.)

A--0 to 2 inches; brown (7.5YR 4/4) gravelly fine sandy loam, dark brown (7.5YR 3/4) moist; weak thin platy structure; soft, very friable, nonsticky and nonplastic; many fine and very fine roots; common very fine vesicular and common fine and very fine tubular pores; 10 percent gravel and 5 percent cobble; strongly effervescent, 6 percent calcium carbonate equivalent; moderately alkaline (pH 8.0); abrupt smooth boundary. (1 to 2 inches thick)

Bk--2 to 14 inches; brown (7.5YR 5/4) gravelly loam, brown (7.5YR 4/4) moist; weak fine subangular blocky structure; slightly hard, friable, slightly sticky and slightly plastic; common fine and very fine roots; common fine and very fine tubular and interstitial pores; 25 percent gravel and hardpan fragments; violently effervescent, common fine irregular calcium carbonate nodules, 7 percent calcium carbonate equivalent; moderately alkaline (pH 8.2); abrupt smooth boundary. (9 to 18 inches thick)

Bkkm--14 to 18 inches; indurated, calcium carbonate cemented petrocalcic; abrupt smooth boundary. (4 to 6 inches thick)

B'k--18 to 22 inches; pinkish white (7.5YR 8/2) and pinkish gray (7.5YR 7/2) gravelly loam, pink (7.5YR 8/4) and pink (7.5YR 7/4) moist; weak fine subangular structure; slightly hard, friable, slightly sticky and slightly plastic; very few fine and very fine roots; common fine interstitial pores; 20 percent gravel and hardpan fragments; violently effervescent, weakly calcium carbonate cemented, 39 percent calcium carbonate equivalent; moderately alkaline (pH 8.4); abrupt smooth boundary. (4 to 10 inches thick)

B'km--22 to 24 inches; indurated, calcium carbonate cemented petrocalcic; abrupt smooth boundary. (2 to 4 inches thick)

B''k--24 to 48 inches; pinkish white (7.5YR 8/2) and pinkish gray (7.5YR 7/2) gravelly loam, pink (7.5YR 8/4) and pink (7.5YR 7/4) moist; massive; hard, firm, slightly sticky and slightly plastic; no observed roots; common fine tubular pores; 20 percent gravel and hardpan fragments; violently effervescent, weakly calcium carbonate cemented, 32 percent calcium carbonate equivalent; moderately alkaline (pH 8.4); abrupt irregular boundary. (10 to 30 inches thick)

2R--48 inches; basalt.

TYPE LOCATION: Mohave County, Arizona; about 7.6 miles south of the Arizona-Utah state line and 16.8 miles east of the Arizona-Nevada state line; 400 feet south and 1000 feet west of the northwest corner of section 12, T.40 N., R.14 W.; 36 degrees, 53 minutes, 26 seconds North latitude and 113 degrees, 44 minutes, 33 seconds West longitude.

RANGE IN CHARACTERISTICS:

Soil Moisture: Intermittently moist in some part of the soil moisture control section during July - September and December - February. Driest during May and June. Ustic aridic soil moisture regime.

Rock Fragments: 15 to 35 percent gravel

Soil Temperature: 52 to 58 degrees F.

Organic Matter: less than 1 percent in the surface horizon

Depth to Calcic: 1 to 5 inches

Depth to Petrocalcic: 10 to 20 inches

Depth to bedrock: 25 to 60 inches

A horizon
Hue: 10YR, 7.5YR
Value: 4 through 6 dry, 3 through 5 moist
Chroma: 2 through 4, dry or moist
Calcium carbonate equivalent: 1 to 10 percent
Rock fragments: 0 to 5 percent cobble, 15 to 30 percent gravel

Bk horizon
Hue: 10YR, 7.5YR
Value: 5 through 8 dry, 4 through 7 moist
Chroma: 2 through 4, dry or moist
Texture: loam, fine sandy loam, sandy loam (7 to 18 percent clay)
Reaction: moderately or strongly alkaline
Calcium carbonate equivalent: 5 to 40 percent
Rock fragments: 15 to 35 percent gravel

Bkm and B' horizons
Alternating, indurated petrocalcic horizons and unconsolidated soil material

COMPETING SERIES: These are the Cardenas (NM), Limeridge (UT) and Shafter (NV) series. Cardenas and Shafter soils do not have bedrock below the hardpan. Limeridge soils have limestone bedrock below the hardpan. In addition, Cardenas soils are in the Western Great Plains (LRR-G MLRA 70) and are moist in May and June. In addition, Shafter soils are in the Great Salt Lake Area (LRR-D MLRA 28A) have a typic aridic moisture regime (mean annual precipitation is 6 to 8 inches) with cool, moist winters and warm, dry summers.

GEOGRAPHIC SETTING: Pocum soils are on mesas and have slopes of 1 to 10 percent. These soils formed in colluvium and alluvium derived dominantly from basalt and other volcanic rocks. Elevations range from 4,800 to 6,000 feet. The mean annual air temperature is 50 to 56 degrees F. Mean annual precipitation is 10 to 14 inches. The frost-free period is 135 to 165 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Luzena, Delenbaw, Springerville, and Yellowhorse soils. Luzena soils contain more than 18 percent clay and have a lithic contact within 20 inches of the surface. Delenbaw soils contain more than 35 percent coarse fragments and are very deep. Springerville and Yellowhorse soils are fine textured.

DRAINAGE AND PERMEABILITY: Well drained; slow to medium runoff; moderate permeability.

USE AND VEGETATION: Pocum soils are used for livestock grazing and wildlife habitat. The present vegetation is big sagebrush, juniper, blackbrush, black grama, blue grama, and galleta.

DISTRIBUTION AND EXTENT: Northwestern Arizona. This series is of small extent. MLRA is 35.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona

SERIES ESTABLISHED: Mohave County, Arizona; Soil survey of Shivwits Area, Arizona, Part of Mohave County; 1994.

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

Ochric epipedon - the zone from 0 to 2 inches (A horizon)

Calcic horizon - the zone from 2 to 14 inches (Bk horizon)

Petrocalcic horizon - the zone from 14 to 18 inches (Bkm horizon)

Lithic contact - the boundary at 48 inches (2R horizon)

Classified according to Soil Taxonomy, Second Edition, 1999; Keys to Soil Taxonomy, Eleventh Editon, 2010

Formerly classified as Ustochreptic Paleorthids.

Update and revisions for the correlation of Wupatki National Monument, AZ, June 2013

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National Cooperative Soil Survey
U.S.A.