LOCATION GUNSIGHT AZ

Established Series
Rev. EGC/MSJ/YHH
08/2018

GUNSIGHT SERIES

The Gunsight series consists of very deep, somewhat excessively drained, strongly calcareous soils that formed in alluvium from mixed sources. Gunsight soils are on fan terraces or stream terraces and have slopes of 0 to 60 percent. The mean annual precipitation is about 7 inches. Mean annual air temperature is about 71 degrees F.

TAXONOMIC CLASS: Loamy-skeletal, mixed, superactive, hyperthermic Typic Haplocalcids

TYPICAL PEDON: Gunsight very gravelly loam - rangeland. (Colors are for dry soil unless otherwise noted.) 50 to 60 percent of surface is covered with gravel.

A--0 to 2 inches; light brown (7.5YR 6/4) very gravelly loam, brown (7.5YR 4/4) moist; weak medium platy structure; slightly hard, very friable, nonsticky and slightly plastic; few very fine roots; many very fine and fine irregular pores; 50 percent gravel; strongly effervescent; moderately alkaline (pH 8.2); abrupt smooth boundary. (2 to 4 inches thick)

Bw--2 to 10 inches; pink (7.5YR 7/4) very gravelly loam, brown (7.5YR 5/4) moist; massive; slightly hard, friable, nonsticky and slightly plastic; few fine and medium roots; common very fine irregular pores; 50 percent gravel; violently effervescent; few fine calcium carbonate filaments; moderately alkaline (pH 8.3); clear wavy boundary. (8 to 16 inches thick)

Bkk1--10 to 18 inches; white (N 8/) and pinkish gray (7.5YR 7/2) extremely gravelly loam, pinkish gray (7.5YR 7/2) and brown (7.5YR 5/4) moist; massive; hard, friable, slightly sticky and slightly plastic; few fine and medium roots; common very fine irregular pores; 70 percent calcium carbonate coated gravel; violently effervescent; many large calcium carbonate masses; strongly alkaline (pH 8.5); gradual wavy boundary. (6 to 10 inches thick)

Bkk2--18 to 32 inches; pinkish white (7.5YR 8/2), pinkish gray (7.5YR 7/2) and pink (7.5YR 7/4) extremely gravelly sandy loam, pinkish gray (7.5YR 7/2) and brown (7.5YR 5/4) moist; massive; hard, friable, slightly sticky and moderately plastic; few very fine roots; common very fine irregular pores; 75 percent calcium carbonate coated gravel; violently effervescent; many large calcium carbonate masses; moderately alkaline (pH 8.3); gradual wavy boundary. (12 to 20 inches thick)

Bkk3--32 to 60 inches; pinkish white (7.5YR 8/2), pinkish gray (7.5YR 7/2) and pink (7.5YR 7/4) very gravelly loam, pinkish gray (7.5YR 7/2) and brown (7.5YR 5/4) moist; massive; hard, friable, slightly sticky and moderately plastic; common very fine irregular pores; 40 percent calcium carbonate coated gravel; violently effervescent; many large calcium carbonate masses; moderately alkaline (pH 8.3).

TYPE LOCATION: Pima County, Arizona; Organ Pipe Cactus National Monument Area; 2,640 feet south and 1,400 feet east of the northwest corner of section 1, T. 18 S., R. 5 W. Latitude of 31 degrees, 53 minutes, 17 seconds N., Longitude of 112 degrees, 44 minutes, 21 seconds W., NAD 83.

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. Typic aridic soil moisture regime.

Soil temperature - 72 to 78 degrees F.

Depth to calcic horizon - 3 to 20 inches

Calcium Carbonate - 5 percent or more calcium carbonate equivalent in the calcic horizon. Occurs as small to large masses or nodules; weakly to strongly cemented in some pedons.

Rock fragments - Averages more than 35 percent in the control section. Some subhorizons have as much as 80 percent. Predominantly 1/2 to 3 inches in diameter. Some areas have a desert pavement with a moderate patina.

Reaction - Moderately or strongly alkaline

Sodicity - Nonsodic to strongly sodic

Texture - Fine sandy loam, sandy loam, loam in the particle-size control section. A few thin strata of less gravelly material occur in some pedons. Averages less than 18 percent clay.

A horizon
Hue: 7.5YR, 10YR
Value: 6, 7 or 8 dry, 4 or 5 moist
Chroma: 2 through 6, dry or moist

Bw horizon
Hue: 7.5YR, 10YR
Value: 5, 6 or 7 dry, 4 or 5 moist
Chroma: 3 or 4, dry or moist

Bk horizon
Hue: 7.5YR, 10YR
Value: 5 through 8 dry, 4 through 8 moist
Chroma: 2 through 4, dry or moist

COMPETING SERIES: These are the Chemehuevi (CA), Heleweiser (NV), Oldswede (T)(CA), and Supplymine (T)(CA) series. Chemehuevi soils have less than 15 percent calcium carbonate equivalent in the upper part of the calcic horizon and have secondary accumulations of silica and gypsum in the lower part of the calcic horizon. Heleweiser soils have gypsum in the lower part of the profile. Oldswede and Supplymine do not have OSDs and cannot be competed.

GEOGRAPHIC SETTING: Gunsight soils are on stream terraces or fan terraces. They formed in stratified alluvium from mixed sources. Slopes are dominantly 1 to 25 percent, but range from 0 to 60 percent. Elevations are 400 to 2600 feet. The climate is hot, arid and continental. Mean annual precipitation is 2 to 10 inches occurring as summer thunderstorms and gentle winter rains. Mean annual air temperature is 68 to 76 degrees F. The frost-free period is about 240 to 350 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Chuckawalla, Cipriano, Ebon, Harqua, Tremant and the similar Rillito soils. Chuckawalla, Ebon, Harqua and Tremant soils have argillic horizons. Cipriano soils have a duripan. Rillito soils have 15 to 35 percent gravel.

DRAINAGE AND PERMEABILITY: Somewhat excessively drained; very low to high runoff; moderate or moderately rapid permeability.

USE AND VEGETATION: Used for livestock grazing and recreation. The vegetation is creosotebush, ocotillo, paloverde, saguaro, cholla, and triangle bursage.

DISTRIBUTION AND EXTENT: Southwest and south central Arizona. The series is extensive. Total extent is about 585,000 acres. MLRA is 40.

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

SERIES ESTABLISHED: Pima County, Arizona; Soil Survey of Organ Pipe Cactus-Cabeza Prieta Area, Arizona, Parts of Pima and Yuma Counties, 1971.

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 10 to 40 inches (Bk1, Bk2, Bk3 horizons)

Classified according to Soil Taxonomy, Second Edition, 1999; Keys to Soil Taxonomy, Tenth Edition, 2006.

Revised for the correlation of AZ661, 2/2009, WWJ

National Cooperative Soil Survey
U.S.A.