Grassland is a relatively common landcover within Napa County, covering over 53,700 acres or nearly 11% of the county. Grassland species composition is highly diverse and provide habitat for a number of reptiles, mammals, and birds. Large grassland areas are most common in the southeastern portion of the County, around the cities of American Canyon and the valley floor of Napa.

Three types of grassland assemblages exist within Napa County:

  • Annual grassland
  • Native grassland
  • Serpentine (bunchgrass) grassland

Annual grassland is an herbaceous plant community dominated by nonnative annual grasses such as wild oat (Avena), brome (Bromus) grasses, and wild barley (Hordeum) species.

Native grassland is dominated by a mixture of annual and perennial grasses such as small fescue (Vulpia microstachys), purples needlegrass (Nasella pulchra), and nodding needlegrass (Nasella cernua).

Serpentine (bunchgrass) grassland occurs on soils derived from serpentine and generally has less overall vegetation cover. Bunchgrasses typically occur in patches and are primarily dominated by medusa head, goatgrass (Aegilops triuncialis) and foxtail brome (Bromus madritensis). 

A variety of different plants that grow in Napa County grasslands are shown below.




Italian ryegrass

Lolium multflorum


 Medusa head

Taeniantherum caput-medusae


The western fence lizard (Sceloporus occidentalis), common garter snake (Thamnophis sirtalis), and gopher snake (Pituophis catenifer) are a few examples of the variety of reptiles found in grassland. Mammals typically found in grassland habitats include the black-tailed jackrabbit (Lepus californicus), California ground squirrel (Spermophilus beecheyi), western harvest mouse (Reithrodontomys megalotis), and coyote (Canis latrans). Grassland provide breeding habitats for birds including the western kingbird (Tyrannus verticalis), loggerhead shrike (Lanis ludovicianus), California horned lark (Eremophila alpestris actia) and the western bluebird (Sialia mexicana).

Reptiles and Amphibians

Western fence lizard

Sceloporus occidentalis


Garter snake 

Thomnophis sirtalis


Gopher snake

Pituophis catenfornifer



California horned lark

Eremophila alpestris actia

Loggerhead shrike

Lanius ludovicianus

Western kingbird

Tyrannus verticalis



California ground squirrel

Spermophilus beecheyi

Black-tailed jackrabbit

Lepus californicus


Canis latrans

The primary ecosystem functions of grassland in the County are:

  • Maintain water quality through soil retention and by filtering out sediment and nutrients from run-off
  • Prevent flooding and minimize channel erosion by slowing surface runoff
  • Increase infiltration to groundwater
  • Provide habitat
  • Provide fodder for grazing livestock
  • Provide opportunities for recreation, including but not limited to hunting, bird-watching, hiking, horseback riding, and OHV use

These functions are enhanced when the key characteristics of grassland habitats are comprised of high-cover herbaceous vegetation, a low-cover of woody vegetation, and low to moderate levels of disturbance.

Use the map below to explore the various biotic communities throughout Napa County.