Natural Resources
Conservation Service
Ecological site R018XA104CA
Shallow Mesic Volcanic Ridges
Last updated: 4/24/2024
Accessed: 04/26/2024
General information
Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
MLRA notes
Major Land Resource Area (MLRA): 018X–Sierra Nevada Foothills
Major Land Resource Area (MLRA) 18, Sierra Nevada Foothills is located entirely in California and runs north to south adjacent to and down-slope of the west side of the Sierra Nevada Mountains (MLRA 22A). MLRA 18 includes rolling to steep dissected hills and low mountains, with several very steep river valleys. Climate is distinctively Mediterranean (xeric soil moisture regime) with hot, dry summers, and relatively cool, wet winters. Most of the precipitation comes as rain; average annual precipitation ranges from 15 to 55 inches in most of the area (precipitation generally increases with elevation and from south to north). Soil temperature regime is thermic; mean annual air temperature generally ranges between 52 and 64 degrees F. Geology is rather complex in this region; there were several volcanic flow and ashfall events, as well as tectonic uplift, during the past 25 million years that contributed to the current landscape.
LRU notes
The Tuscan Flows LRU is the northernmost Land Resource Unit in MLRA 18. It occurs down slope of and is geologically related to the southern Cascades; however, its inclusion in MLRA 18 stems from the ecosystem’s close resemblance to other Sierra Nevada Foothill systems. This LRU is situated on a low elevation volcanic plateau at the northeast end of the Sacramento Valley. The geology includes, but not limited to late Pliocene and Quartenary basalt, andesite and andesitic lahars (mudflows). Several cinder cones dot the landscape and active fluvial processes are occurring in the larger canyons. Elevation ranges between 250 and 2000 feet above sea level on the main plateau, but can range as high as 3000 feet on the highest hills. Precipitation is among the highest in MLRA 18, ranging from 30 to 55 inches annually. Mean annual air temperature ranges between 56 and 62 F. Frost free days (generally exhibiting an inverse relationship with elevation) range from 184 to 282 days.
Classification relationships
CLASSIFICATION RELATIONSHIPS
This site is located within M261F, the Sierra Nevada Foothills Section, (McNab et al., 2007) of the National Hierarchical Framework of Ecological Units (Cleland et al., 1997), M261Fa, the Tuscan Flows Subsection.
Level III and Level IV ecoregions systems (Omernik, 1987, and EPA, 2011) are: Level III, Central California Foothills and Coastal Mountains and Level IV, Ecoregion 6a, Tuscan Flows.
Ecological site concept
This site is characterized by shallow soils derived from residuum on volcanic breccia. It occurs on narrow volcanic ridges and steep sideslopes of hills, mountains, and canyons. The soil temperature regime is mesic. Slope gradient typically ranges from 5 to 45%. Mean annual precipitation typically ranging from 36 to 54 inches, and elevations range from 1285 to 1800 feet.
The overriding abiotic factors on this site are shallow, rocky soils which restrict the establishment of coniferous forests, even though the effective precipitation in the area is favorable to timber production. The most common soil correlated to this ecological site is Rockstripe (Loamy-skeletal, mixed, active, nonacid, mesic Lithic Xerorthents). Rockstripe soils are very shallow, somewhat poorly drained soils which formed in residuum derived from volcanic mudflow breccia. Due to very shallow depth and poor drainage, shrub and tree densities are usually lower than in adjacent, well drained soils.
This vegetation community consists of annual grasses and forbs, oak savannahs with low to moderate densities of scrub oak (Quercus berberdifolia) and canyon live oak (Quercus chrysolepis), and in the absence of disturbance, chaparral. Dominant annual grasses for this site include soft brome (Bromus hordeaceus), wild oat (Avena fatua), and bristly dogtail grass (Cynosurus echinata). Forbs include pink (Silene spp.) and fillaree (Erodium spp.). Common shrubs include manzanita species (Arctostaphylos spp.), ceanothus species, and poison oak (Toxicodendron diversilobum).
Associated sites
| F018XA202CA |
Deep Mesic Mountain Slopes & Summits This site commonly occurs nearby. |
|---|
Table 1. Dominant plant species
| Tree |
(1) Quercus berberidifolia |
|---|---|
| Shrub |
(1) Ceanothus |
| Herbaceous |
(1) Bromus hordeaceus |
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