LOCATION AJOLITO AZEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, hyperthermic, shallow Argic Petrocalcids
TYPICAL PEDON: Ajolito extremely gravelly sandy loam - rangeland. (Colors are for dry soil unless otherwise noted.) 90 percent of the surface is covered with rounded, darkly varnished gravel and pan fragments.
A--0 to 1 inch; light brown (7.5YR 6/4) extremely gravelly sandy loam, brown (7.5YR 4/4) moist; weak very fine granular structure; soft, very friable, nonsticky and nonplastic; many very fine vesicular pores; violently effervescent; 75 percent rounded gravel; slightly alkaline (pH 7.6); abrupt smooth boundary. (1 to 2 inches thick)
Btk1--1 to 5 inches; light reddish brown (5YR 6/4) very gravelly fine sandy loam, light reddish brown (5YR 6/4) moist; weak medium subangular blocky structure; soft, very friable, slightly sticky and slightly plastic; common very fine roots; common very fine tubular pores; few distinct clay films on faces of peds, common thin calcium carbonate accumulations in pores and as coatings on gravel; violently effervescent; 40 percent rounded gravel; slightly alkaline (pH 7.6); clear smooth boundary. (1 to 7 inches thick)
Btk2--5 to 14 inches; light reddish brown (5YR 6/4) very gravelly coarse sandy loam, yellowish red (5YR 4/6) moist; weak medium subangular blocky structure; soft, very friable, nonsticky and nonplastic; few fine tubular pores; few distinct clay films on faces of peds; thick calcium carbonate coatings on gravel; violently effervescent; very slightly saline (EC 3.7 dS/m); 50 percent rounded gravel; slightly alkaline (pH 7.8); abrupt smooth boundary. (2 to 11 inches thick)
2Bkm--14 to 32 inches; calcium carbonate cemented and indurated hardpan.
TYPE LOCATION: Maricopa County, Arizona; about 10 miles west and 7 miles north of Gila Bend; 1900 feet west and 2400 feet south of the northeast corner of section 6, T. 5 S., R. 6 W. Lat.33 degrees 1 minute 17 seconds N and long. 112 degrees 54 minutes 55 seconds W., NAD 83.
RANGE IN CHARACTERISTICS:
Soil moisture: Intermittently moist in some part of soil moisture control section during July-September and December-February. Driest during May and June. Typic aridic soil moisture regime.
Soil temperature - 72 to 76 degrees F.
Depth to petrocalcic: 4 to 20 inches
Rock fragments: About 85 to 100 percent of the surface is covered with darkly varnished rounded gravel (desert pavement); 20 to 85 percent in any one horizon; averages 35 to 75 percent in the particle-size control section; are water-rounded.
A horizon
Hue: 7.5YR, 10YR
Value: 6 or 7 dry, 4 or 5 moist
B horizon
Hue: 5YR, 7.5YR
Value: 5, 6, or 7 dry, 4, 5, or 6 moist
Chroma: 3, 4, or 6, dry or moist
Texture: Loam, sandy loam, fine sandy loam, coarse sandy loam (5 to 15 percent clay)
Reaction: slightly alkaline or moderately alkaline
Salinity: pedons are typically non-saline or slightly saline. Some pedons are strongly saline in the surface crust and just above the petrocalcic horizon.
Cementation: cemented principally with calcium carbonate
COMPETING SERIES: There are no competing series.
GEOGRAPHIC SETTING: Ajolito soils are on stream terraces. Slope ranges from 1 to 5 percent. Elevations range from 400 to 1000 feet. They formed in Quaternary (Pleistocene) stream alluvium. The mean annual precipitation is 5 to 7 inches occurring as summer thunderstorms and gentle winter rain. Mean annual air temperature is 70 to 74 degrees F. and the frost-free period is about 260 to 320 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Carrizo, Gunsight, Tucson and the similar Chuckawalla soils. Carrizo soils are sandy-skeletal and are on adjacent flood plains. Gunsight soils are very deep and slightly lower. Tucson soils are very deep, loamy, and on adjacent terraces. Chuckawalla soils are very deep and have dark desert pavements.
DRAINAGE AND PERMEABILITY: Somewhat excessively drained; rapid runoff; permeability is moderately rapid above the pan.
USE AND VEGETATION: Used for livestock grazing and wildlife habitat. Native vegetation is mainly turkshead. Annual forbs and grasses and occasional creosotebush grow where the desert pavement is disturbed.
DISTRIBUTION AND EXTENT: Southern Arizona. This series is not extensive. Total extent is about 2,800 acres. MLRA is 40.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Gila Bend-Ajo Area, Arizona, Parts of Maricopa and Pima Counties; 1985.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from 0 to 1 inch (A horizon)
Argillic horizon - The zone from 1 to 14 inches (Btk1, Btk2 horizons)
Petrocalcic horizon - The zone below 14 inches (2Bkm horizon)
Classified according to Soil Taxonomy, Second Edition, 1999, and Keys to Soil Taxonomy, Tenth Edition, 2006.
Revised for the correlation of AZ661, 11/08, PDC.