LOCATION ALVISO CA

Established Series
Rev. RCH/LCL/ET
09/2025

ALVISO SERIES

The Alviso series consists of very deep, very poorly drained soils that formed in alluvium from sedimentary rocks. Alviso soils are in tidal flats, tidal marshes, and sloughs in basin floors and estuaries. Slopes range from 0 to 2 percent. The Alviso series have gray, neutral, silty clay loam A horizons and light gray, gleyed, mildly alkaline, silty clay loam and silty clay upper C horizons, and greenish gray very fine sand lower C horizons. The mean annual precipitation is about 17 inches (425 mm) and the mean annual air temperature is about 57 degrees F (14 degrees C).

TAXONOMIC CLASS: Fine, mixed, superactive, nonacid, isomesic Typic Fluvaquents

TYPICAL PEDON: Alviso silty clay loam - marsh, at an elevation of 0 feet (0 m). (Colors are for dry soil unless otherwise stated.)

Oi--0 inches (0cm); discontinuous layer of plant remains. (0 to 1 inch (0 to 2 cm) thick)

Ag--0 to 5 inches (5 to 13 cm); gray (5Y 5/1) silty clay loam, dark olive gray (5Y 3/2) moist; moderate medium angular blocky structure; hard, friable, sticky, plastic; few fine and common very fine roots; few very fine interstitial and very fine tubular pores; neutral (pH 7.2); gradual smooth boundary. (4 to 7 inches (10 to 18 cm) thick)

C1g--5 to 14 inches (13 to 36 cm); gray (5Y 6/1) silty clay loam, dark gray (5Y 4/1) moist; common fine brown (7.5YR 5/4) mottles; moderate medium angular blocky structure; hard, friable, sticky, plastic; many very fine and fine roots; common very fine and fine roots; common very fine and few fine tubular pores; slightly alkaline (pH 7.8); clear smooth boundary. (6 to 12 inches (15 to 30 cm) thick)

C2g--14 to 45 inches (36 to 114 cm); mixed gray (N 6/, 5/) and light gray (N 7/) silty clay, dark gray (5Y 4/1) moist; common medium distinct olive (5Y 5/3) moist mottles; moderate medium angular blocky structure; very hard, friable, sticky, plastic; common very fine roots; few very fine and fine tubular pores; layer or organic material 1/2 inch thick near top of horizon, several very dark gray (5Y 3/1) moist and dark greenish gray (5G 4/1) moist seams 1/8 to 1/2 inch thick, color becomes more greenish in lower portion of horizon; few small 2 to 5 mm concretions; slightly alkaline (pH 7.8); gradual boundary. (10 to 40 inches (25 to 102 cm) thick)

2Cg--45 to 60 inches (114 to 152 cm); greenish gray (5GY 6/1) very fine sand, greenish black (5BG 2/1) moist; massive; slightly hard, very friable, slightly sticky and slightly plastic; many very fine interstitial pores; slightly acid (pH 6.4).

TYPE LOCATION: Monterey County, California; 1 mile south of Moss Landing on Tembladero Slough; 4/10 mile west on Potrero Road, from Moss Landing Road, and 660 feet north (100 feet beyond dike).

RANGE IN CHARACTERISTICS: The water table is close enough to the surface that the upper horizons are always moist. The soil may be flooded by sea water at high tide or during high stream flows coinciding with high tides. The mean soil temperature is about 57 degrees F (14 degrees C), the average July soil temperature is about 59 degrees F (15 degrees C) and the average January soil temperature is about 52 degrees F (11 degrees C). Fine stratification is absent from the upper part of the profile. Coarse stratification is common and the organic matter decreases irregularly with depth.

The A horizon is less than 7 inches (18 cm) thick or has less than 1 percent organic matter after mixing to 7 inches (18 cm). Distinct or prominent mottles are in or immediately below the A horizon. This horizon is gray to dark gray and is neutral or has 10YR or 5Y hue. It ranges from neutral to moderately alkaline.

The upper part of the C horizon ranges from light gray to greenish gray (5Y and 5GY hues) with distinct to prominent, brown to olive mottles (7.5YR and 5Y hues). It is silty clay loam to silty clay and usually is stratified with thin layers of organic material and lenses of coarser textured material. The particle size control section (10 to 40 inches (25 to 100 cm)) averages 35 to 45 percent clay. This horizon is neutral to moderately alkaline and is calcareous in some pedons. The lower part of the C horizon has strong gley colors in 5GY, 5BG or 5B hue. It ranges from silty clay to sand, but is usually sandy. It is slightly acid to moderately alkaline.

COMPETING SERIES: These are the Langlois series. Langlois soils (MLRA 1) are moderately to strongly acid throughout the upper part of the control section, and slightly to moderately acid in the lower part.

GEOGRAPHIC SETTING: The Alviso soils occur near sea level in level basins and tidal flats with branched meandering channels that are flushed by sea water and varying amounts of fresh water. They formed in alluvium dominantly from sedimentary rocks. The climate is subhumid, mesothermal with cool foggy summers and cool, moist winters. Mean annual rainfall is 12 to 21 inches. Mean annual air temperature is about 57 degrees F (14 degrees C), average January air temperature about 49 degrees F (9 degrees C), and average July air temperature about 57 to 59 degrees F (14 to 15 degrees C). The average frost-free season is 330 to 365 days.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Antioch, Camarillo, Clear Lake, Pescadero, and Tamba soils and the competing Reyes soils. Antioch soils lack high water table and mottles. Camarillo soils have no mottles above depth of 20 inches (50 cm). Clear Lake soils have cracks and slickensides. Pescadero soils have natric horizons. Tamba soils are strongly acid.

DRAINAGE AND PERMEABILITY: Very poorly drained; very slow runoff; slow permeability. Ares not diked are periodically flooded during high tides.

USE AND VEGETATION: Used mainly for recreation and very limited grazing. Diked areas have been reclaimed and are used for pasture and growing artichokes. Vegetation is mostly pickleweed, inkweed, saltgrass, and other salt-tolerant plants.

DISTRIBUTION AND EXTENT: The soils occur around San Francisco Bay and other tidal flats of California. The soils are inextensive.

SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: Davis, California

SERIES ESTABLISHED: Salinas Area, California, 1925.

REMARKS: The soils were formerly classified as Low Humic Gray soils.

The classification was updated in February 2001 using the Eighth Edition to Soil Taxonomy. This series was formerly classified as Fine, mixed, nonacid, isomesic Tropic Fluvaquents. Competing series were not checked at that time.

Last major revision by the state on 5/72.
09/2025--Competing series checked and updated. -JBB

National Cooperative Soil Survey
U.S.A.