LOCATION PLUTO                   AZ

Established Series
Rev. JMH/CRF/MJA
02/2025

PLUTO SERIES

The Pluto series consists of moderately deep or deep, well drained soils that formed in residuum derived from basalt. Pluto soils are on the plains of lava fields. Slopes range from 0 to 15 percent. Mean annual precipitation is about 20 inches and the mean annual temperature is about 48 degrees F.

TAXONOMIC CLASS: Fine, smectitic, mesic Typic Argiustolls

TYPICAL PEDON: Pluto-Grandwash complex (Colors are for dry soil unless otherwise noted.)

Oi--0 to 0.3 inches (0 to 1 cm); slightly decomposed plant material

A--0.3 to 3 inches (1 to 10 cm); brown (7.5YR 4/3) loam, dark brown (7.5YR 3/2) moist; weak fine subangular blocky; soft, very friable, nonsticky, nonplastic; few very fine and fine dendritic tubular pores; common very fine and fine roots throughout; 1 percent cobbles; noneffervescent; neutral (pH 7.2); abrupt smooth boundary

Btss1--3 to 22 inches (10 to 46 cm); brown (7.5YR 4/2) clay loam, dark brown (7.5YR 3/2) moist; moderate medium subangular blocky; very hard, firm, moderately sticky, moderately plastic; few very fine and fine dendritic tubular pores; few very fine, few fine, and common coarse roots throughout; 30 percent prominent clay films on all faces of peds; 3 percent cobbles; very slight effervescence; slightly alkaline,( pH 7.6); clear smooth boundary

Btss2--22 to 28 inches (46 to 71 cm); brown (7.5YR 4/3) clay, dark brown (7.5YR 3/4) moist; moderate medium angular blocky; very hard, firm, very sticky, very plastic; few very fine and fine dendritic tubular pores; common coarse roots throughout; 40 percent prominent clay films on all faces of peds; 5 percent gravel; slight effervescence; slightly alkaline (pH 7.8); clear smooth boundary

Btss3--28 to 45 inches (71 to 114 cm); yellowish red (5YR 4/6) clay loam, reddish brown (5YR 4/4) moist; moderate medium angular blocky; extremely hard, very firm, moderately sticky, moderately plastic; few very fine and fine irregular pores; 35 percent prominent clay films on all faces of peds;7 percent gravel; slight effervescence; moderately alkaline (pH 8.0); clear smooth boundary

R--45 to 55 inches (114 to 139 cm), basalt bedrock

TYPE LOCATION: Coconino County, Arizona; located about 0.5 kilometers (0.3 miles) northeast of Chalender townsite, Arizona; USGS Quadrangle Davenport Hill; Latitude 35.236994, Longitude -112.0226213, Datum WGS84.

RANGE IN CHARACTERISTICS:
Soil moisture regime: typic ustic
Mean annual soil temperature: 46 to 50 degrees F
Rock fragment content: 0 to 15 percent
Depth to lithic contact: over 50 centimeters
Particle-size control section:
Clay content: 35 to 60 percent

A horizon
Hue: 5YR or 7.5YR
Value: 4 or 5 (2 or 3 moist)
Chroma: 2 or 3, dry or moist
Calcium carbonate equivalent: 0 to 2 percent
Reaction: neutral or slightly alkaline

B horizon
Hue: 5YR or 7.5YR
Value: 4 or 5, (3 or 4 moist)
Chroma: 2 to 6, (2 to 4 moist)
Texture: clay
Calcium carbonate equivalent: 0 to 2 percent
Sodium Adsorption Ratio (SAR): 0 to 2
Reaction: neutral or slightly alkaline

COMPETING SERIES: These are the Beadle, Boulder, Brolliar, Carlson, Harney, McClure, Mento, Raber, Reliance, and Spearville series. Beadle, Boulder, Carlson, Harney, McClue, Mento, Raber soils are frequently moist in May and June. Brolliar series has been mapped in frigid temperatures and will be returned to frigid taxonomy.

GEOGRAPHIC SETTING:
Parent material: residuum derived from basalt
Landform: lava fields
Slopes: 0 to 15 percent
Elevation: 6,500 to 7,400 feet
Mean annual air temperature: 45 to 49 degrees F
Mean annual precipitation: 18 to 22 inches
Precipitation peaks in July and August, and in winter months. May and June are much drier.
Frost-free period: 100 to 120 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Purpleheart, Procky, and Grandwash soils. Purpleheart soils are in lower positions on broad sloping surfaces. Procky soils are colluvial soils over residuum near slope breaks. Grandwash soils are in shallow residuum at erosional positions of shoulders and sideslopes of hills.

DRAINAGE AND PERMEABILITY: well drained, slow permeability

USE AND VEGETATION: These soils are used principally as habitat for wildlife. Native vegetation is mainly ponderosa pine, Gambel oak, spike muhly, mountain muhly, Arizona fescue, and alligator juniper.

DISTRIBUTION AND EXTENT: Northern Arizona. MLRA 39.

MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Davis, California.

SERIES ESTABLISHED: Coconino County, Arizona.

REMARKS:
Diagnostic horizons and features recognized in this pedon are:
Mollic epipedon: from 0 to 46 centimeters. (A, Btss horizons)
Argillic horizon: from 10 to 71 inches. (Btss horizons). Pressure faces occur in many profiles
The soil is found in the vicinity of Observatory Mesa where minor planet Pluto was first discovered. The minor planet is the source of the name.
Taxonomic Version: Keys to Soil Taxonomy, Thirteenth Edition, 2022
________________________________________

---

National Cooperative Soil Survey
U.S.A.