LOCATION LETRADO NMTentative Series
TAXONOMIC CLASS: Fine-loamy, mixed, superactive, mesic Typic Paleustalfs
TYPICAL PEDON: Letrado loam--on a toeslope of an interfluve sloping 14 percent to the north-northeast at 7,324 feet elevation-forestland. (Colors are for dry soil unless otherwise noted. When described on September 11, 2000, the soil was dry throughout.)
A--0 to 1 inch; very dark grayish brown (10YR 3/2) loam, very dark brown (10YR 2/2) moist; weak fine granular structure; soft, very friable, slightly sticky and nonplastic; common fine and many very fine roots; common very fine irregularly shaped pores; 2 percent gravel; neutral (pH 7.2); abrupt smooth boundary. (1 to 3 inches thick)
E--1 to 6 inches; pink (7.5YR 7/3) loam, brown (7.5YR 5/4) moist; moderate fine subangular blocky structure; slightly hard, friable, slightly sticky and nonplastic; common fine and common very fine roots; few fine and few very fine tubular pores; 5 percent paragravel; neutral (pH 6.6); abrupt irregular boundary. (3 to 9 inches thick)
Bt1--6 to 12 inches; strong brown (7.5YR 4/6) clay, brown (7.5YR 4/4) moist; weak coarse prismatic structure parting to strong fine subangular blocky; slightly hard, friable, slightly sticky and nonplastic; few coarse, few medium, common fine, and few very fine roots; few very fine tubular pores; 5 percent paragravel; many prominent clay films on faces of peds; neutral (pH 6.6); clear wavy boundary. (5 to 12 inches thick)
Bt2--12 to 19 inches; brown (7.5YR 5/4) clay loam, strong brown (7.5YR 4/6) moist; moderate medium subangular blocky structure; very hard, firm, moderately sticky and moderately plastic; few medium, common fine, and few very fine roots; common very fine tubular pores; 3 percent paragravel; few prominent and common distinct clay films on faces of peds; neutral (pH 6.8); clear wavy boundary. (7 to 34 inches thick)
Bt3--19 to 27 inches; brown (7.5YR 5/4) clay loam, strong brown (7.5YR 4/6) moist; moderate coarse subangular blocky structure; very hard, firm, moderately sticky and moderately plastic; few fine and few very fine roots; few very fine tubular pores; 2 percent paragravel; few prominent and few distinct clay films on faces of peds; neutral (pH 7.2); abrupt wavy boundary. (7 to 34 inches thick)
Bt4--27 to 52 inches; light brown (7.5YR 6/4) clay loam, brown (7.5YR 4/3) moist; moderate medium prismatic structure parting to moderate medium subangular blocky; very hard, firm, moderately sticky and moderately plastic; few fine and few very fine roots; few very fine tubular pores; 5 percent paragravel; common prominent and few distinct clay films on faces of peds; slightly alkaline (pH 7.4); clear wavy boundary. (0 to 28 inches thick)
Bt5--52 to 75 inches; light brown (7.5YR 6/4) clay loam, brown (7.5YR 4/3) moist; moderate medium subangular blocky structure; hard, friable, moderately sticky and slightly plastic; few very fine roots; few very fine tubular pores; 2 percent paragravel; common distinct clay films on faces of peds; slightly alkaline (pH 7.6); clear wavy boundary. (0 to 27 inches thick)
Bt6--75 to 90 inches; light brown (7.5YR 6/4) gravelly sandy clay loam, brown (7.5YR 4/4) moist; weak coarse subangular blocky structure; slightly hard, friable, moderately sticky and moderately plastic; 15 percent paragravel; few faint clay films on faces of peds and bridging sand grains; slightly alkaline (pH 7.6); abrupt wavy boundary. (0 to 15 inches thick)
Cr--90 inches; moderately cemented tuff bedrock
TYPE LOCATION: Bandelier National Monument, Los Alamos County, New Mexico; about 4 miles south of Los Alamos; USGS Frijoles 7.5 minute topographic quadrangle; Latitude 35 degrees 49 minutes 37.68 seconds North and Longitude 106 degrees 19 minutes 38.43 seconds West, NAD 27.
RANGE IN CHARACTERISTICS:
Soil moisture: The soil moisture control section (SMCS) is moist in all parts from January to May and intermittently moist in some part from June to December. The SMCS is dry in some part 40 to 60 percent of the time when the soil temperature at 20 inches is above 41 degrees F (5 degrees C). The soil moisture regime is typic ustic.
Average annual soil temperature - 47 to 49 degrees F
Depth to base of albic horizon - 6 to 11 inches
Depth to base of argillic horizon - 60 to 80 inches or more
Lithology of pararock fragments: rhyolitic tuff
Particle-size control section weighted averages:
Silicate clay content: 27 to 35 percent
Sand content: 30 to 40 percent
Fine sand and coarser content: 25 to 35 percent
Pararock fragment content: 2 to 5 percent
Volcanic glass content: 5 to 15 percent in the coarse silt plus sand fraction
A horizon
Value: 3 or 4 dry, 2 or 3 moist
Clay content: 8 to 18 percent
Pararock fragments: 2 to 5 percent paragravel
E horizon
Hue: 7.5YR or 10YR
Value: 6 or 7 dry, 4 or 5 moist
Chroma: 1 to 3 dry, 1 to 4 moist
Texture: fine sandy loam or loam
Clay content: 8 to 18 percent
Pararock fragments: 2 to 5 percent paragravel
Bt1 horizon
Hue: 5YR to 10YR
Value: 4 or 5 dry, 3 or 4 moist
Chroma: 2 to 6, dry or moist
Texture: clay, sandy clay, or clay loam
Clay content: 35 to 45 percent
Pararock fragments: 2 to 5 percent paragravel
Lower Bt horizons
Hue: 7.5YR or 5YR
Value: 5 or 6 dry, 3 to 5 moist
Chroma: 4 to 6, dry or moist
Texture: clay loam, sandy clay loam, paragravelly sandy clay loam
Clay content: 27 to 35 percent
Volcanic glass content: 20 to 30 percent in lower horizons
Pararock fragments: 2 to 20 percent paragravel
Reaction: neutral or slightly alkaline
COMPETING SERIES: There are no competing series. A similar soil in another family is the Predawn series. Predawn soils are in an aridic ustic moisture regime and have a strong calcic horizon.
GEOGRAPHIC SETTING: Letrado soils are on toeslopes and footslopes of ?? on undulating plateaus. They formed in slope alluvium derived from rhyolitic tuff of the Quaternary age Bandelier Tuff formation. Slopes are 5 to 15 percent. Elevation ranges from 6,900 to 7,600 feet. The mean annual precipitation is 16 to 20 inches with about 45 percent falling as rain from high-intensity convective thunderstorms between July and September. The mean annual air temperature is 45 to 47 degrees F. The frost-free period is 120 to 140 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Adornado, Rotado, Tocal, and Urioste soils. Adornado soils are ashy-pumiceous, have mollic epipedons, and occur on backslopes and footslopes of undulating plateaus. Rotado soils are fine, moderately deep, and occur on summits of undulating plateaus. Tocal soils are clayey, shallow, and occur on shoulders of undulating plateaus. Urioste soils are ashy, very shallow, and occur on backslopes of undulating plateaus.
DRAINAGE AND PERMEABILITY: Well drained; very high surface runoff; permeability is slow.
USE AND VEGETATION: Letrado soils are used for recreation and wildlife habitat. Present vegetation is ponderosa pine, Gambel oak and mountain muhly.
DISTRIBUTION AND EXTENT: Letrado soils are of small extent on the southwestern Jemez Volcanic Field part of the Southern Rocky Mountain province in northcentral New Mexico. The MLRA is 48A.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Bozeman, Montana.
SERIES PROPOSED: Los Alamos County, New Mexico; Bandelier National Monument Soil Survey, 2000. Letrado is a coined name.
REMARKS: Diagnostic horizons and features recognized in this pedon are:
Ochric epipedon - The zone from 0 to 1 inch. (A horizon)
Albic horizon - The zone from 1 to 6 inches. (E horizon)
Abrupt textural change - The more than doubling of clay content at 6 inches. (E to Bt1 horizons)
Argillic horizon - The zone from 6 to 90 inches. (Bt1, Bt2, Bt3, Bt4, Bt5, and Bt6 horizons)
Pale feature - The increase of 25 percent clay with abrupt boundary. (E to Bt1 horizons)
Particle-size control section - The zone from 6 to 26 inches (Bt1, Bt2, and Bt3 horizons)
Classified according to Soil Taxonomy Second Edition, 1999.