LOCATION TOMBSTONE AZEstablished Series
TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, thermic Ustic Haplocalcids
TYPICAL PEDON: Tombstone very gravelly fine sandy loam - rangeland. (Colors are for dry soil unless otherwise noted.) Surface rocks - 50 to 65 percent of the surface is covered with gravel and cobbles
A--0 to 1 inch; grayish brown (10YR 5/2) very gravelly fine sandy loam, dark grayish brown (10YR 4/2) moist; weak thin platy structure; soft, very friable, nonsticky and nonplastic; few fine roots; few fine tubular pores; 52 percent gravel; strongly effervescent, 13 percent calcium carbonate equivalent; moderately alkaline (pH 8.2); abrupt smooth boundary.
Bk1--1 to 5 inches; dark grayish brown (10YR 4/2) gravelly fine sandy loam, very dark grayish brown (10YR 3/2) moist; massive; soft, very friable, nonsticky and nonplastic; common very fine and fine roots; common fine tubular pores; many distinct calcium carbonate coatings on rock fragments; 21 percent gravel; violently effervescent, 17 percent calcium carbonate equivalent; moderately alkaline (pH 8.2); abrupt smooth boundary.
Bk2--5 to 13 inches; pinkish white (7.5YR 8/2) gravelly sandy loam, pinkish gray (7.5YR 6/2) moist; massive; soft, very friable, nonsticky and nonplastic; common very fine and fine roots; common very fine and fine tubular pores; many distinct calcium carbonate coatings on rock fragments; 21 percent gravel; violently effervescent, 22 percent calcium carbonate equivalent; moderately alkaline (pH 8.2); clear smooth boundary.
Bk3--13 to 27 inches; pinkish gray (7.5YR 7/2) very gravelly sandy loam, pinkish gray (7.5YR 6/2) moist; massive; soft, very friable, nonsticky and nonplastic; common very fine and fine roots; few very fine and fine tubular pores; many distinct calcium carbonate coatings on rock fragments; 47 percent gravel; violently effervescent, 19 percent calcium carbonate equivalent; moderately alkaline (pH 8.2); gradual smooth boundary.
Bk4--27 to 60 inches; pinkish gray (7.5YR 6/2) very gravelly loamy sand, brown (7.5YR 4/2) moist; massive; soft, very friable, nonsticky and nonplastic; few fine roots; common very fine and fine irregular and tubular pores; few prominent calcium carbonate coatings on rock fragments; 38 percent gravel; strongly effervescent, 6 percent calcium carbonate equivalent; moderately alkaline (pH 8.0).
TYPE LOCATION: Cochise County, Arizona; located at a latitude of 32 degrees, 44 minutes, 13 seconds North and a longitude of 109 degrees, 59 minutes, 50 seconds West; about 1,310 feet west and 2,275 feet north of the southeast corner of section 33, Township 19 S., Range 23 E.
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. The epipedon is moist in some part less than 90 days (cumulative) when the soil temperature is above 41 degrees F. in 7 out of 10 years. Ustic aridic soil moisture regime.
Rock Fragments: Averages 35 to 70 percent in the particle-size control section, but ranges from 15 to 90 percent in any one horizon
Soil Temperature: 59 to 70 degrees F.
Depth to calcic horizon: 1 to 20 inches. Is weakly cemented in some pedons
Calcium carbonate equivalent: Averages 20 to 35 percent, but ranges from 5 to 40 percent in any one horizon
A horizon
Hue: 7.5YR, 10YR
Value: 4 through 7 dry, 2 through 5 moist
Chroma: 2 through 4, dry or moist
Bk horizon
Hue: 7.5YR, 10YR
Value: 3 through 8, dry or moist
Chroma: 2, 3 or 4 dry, 1 through 4 moist
Texture: Sandy loam, loam, coarse sandy loam, fine sandy loam (5 to 18 percent clay); can range to include loamy sand and loamy coarse sand below 30 inches.
COMPETING SERIES: These are the Chilicotal (TX), Gallen (NM), Gilland (NM), Polar (TX), and Powerline (AZ) series. Chilicotal soils have 15 to 27 percent clay in the control section. Gallen soils have gypsum accumulations. Polar soils have mean annual precipitation of 16 to 24 inches. Gilland soils are moderately deep to shale and sandstone. In addition, Gallen soils are in the Pecos-Canadian Plains and Valleys (MLRA 70); Polar soils are in the Central Rolling Red Plains (MLRA 78); both soils are moist in May and June. Powerline soils have bedrock at depths of 20 to 40 inches.
GEOGRAPHIC SETTING: Tombstone soils are in the Sonoran and Chihuahuan deserts on fan terraces and stream terraces and have slopes of 1 to 50 percent. These soils formed in fan alluvium from mixed sources. Elevations range from 3,000 to 5,300 feet. The mean annual precipitation is 12 to 16 inches. The mean annual air temperature is 57 to 68 degrees F. The frost-free period is 160 to 250 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Elgin, Pedregosa and Stronghold soils. Elgin soils have argillic horizons. Pedregosa soils are very shallow and shallow to a petrocalcic horizon. Stronghold soils are coarse-loamy.
DRAINAGE AND PERMEABILITY: Somewhat excessively drained; slow runoff; moderately rapid permeability.
USE AND VEGETATION: Tombstone soils are used for livestock grazing and wildlife habitat. Some areas are used for watershed research. The present vegetation is threeawn, black grama, sideoats grama, tarbush, whitethorn, and creosotebush.
DISTRIBUTION AND EXTENT: Central Arizona portion of the Upper Sonoran desert and Southeastern Arizona portion of the Chihuahuan desert. This series is not extensive. MLRA is 38 and 41.
MLRA OFFICE RESPONSIBLE: Phoenix, Arizona
SERIES ESTABLISHED: Pima County, Arizona; Soil survey of Pima County, Arizona, Eastern Part; 1986.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from 0 to 1 inch (A horizon)
Calcic horizon - The zone from 1 to 60 inches (Bk1, Bk2, Bk3, Bk4 horizons)
Classified according to Soil Taxonomy Second Edition, 1999; Keys to Soil Taxonomy Tenth Edition, 2006.
The type location was moved to the Douglas-Tombstone Area in April 2000.