American Canyon

The area covers 1500 acres (607 ha) with an elevation range of 2800-3784 ft (854- 1153 m). The RNA is situated on the southern slope of Pine Mountain, located in the La Panza Range. Its boundaries are defined to the north by Pine Mountain. The east to west ridgeline between San Jose peak and peak 3784 defines its southern boundary. The RNA encompasses the uppermost watershed of American Canyon, ultimately draining into the Salinas River.

Distinctive Features 

This is the only RNA identified to target Coulter pine forest in the Southern Coast Ranges (Central California Coast Ranges ecological section). Additionally, the pine stands provide a mixture of age, density, and serotiny for study. The RNA also contains valley needlegrass grassland, which was formerly extensive throughout the valleys of California but now is much reduced (Holland 1986).

Rare Plants: The RNA contains six CNPS listed species: Arctostaphylos pilosula (CNPS List 1B), Calochortus simulans (CNPS List 4), C. palmeri (CNPS List1B), Malacothamnus niveus (Jepson [Hickman 1993]: Malacothamnus jonesii) (CNPS List 4), Sidalcea hickmanii (CNPS List 1B), and Monardella macrantha ssp. hallii (CNPS List 1B).

Association Types

Coulter Pine Forest/Northern Mixed Chaparral (84140/37110): 1473 acres (596 ha). The representative area for this association type generally fits the Holland classification, although the RNA is depauperate in a few other tree species normally found as associates.

This association occurs on all slopes; however, most slopes in the RNA are south-facing. Coulter pine ranges from a few scattered individual trees to dense stands that suppress the undergrowth. Saplings are found in all but the densest stands. A typical stand contains 379 trees/acre (936 trees/ha) and has a basal area of 0.44 ft²/acre (0.1 m²/ha) and a 77 percent shrub cover. The bulk of the pines were 30-35 years old due to regeneration after the 1939 fire. However, an older stand of trees (125-145 years old) occurs on an east-facing slope of the RNA where most of the trees survived the 1939 fire. Here, tree density is lower (98 trees/acre [242 trees/ha]), while basal area and shrub cover increase (137 ft²/acre [31.4 m²/ha] and 96 percent cover).

Pine is completely missing from 20-25 percent of the area incorporating the association type, leaving only chaparral present. The chaparral cover varies with slope, aspect, and soil depth, predictably densest on north- and east-facing slopes. Overall cover ranges from 50 to 98 percent. Most of the chaparral is mature (50 years old), having last burned in 1939, and is generally species poor. Species here include Adenostoma fasciculatum, Arctostaphylos glandulosa, A. glauca, Quercus dumosa, Q. wislizenii var. frutescens, Ceanothus cuneatus, C. oliganthus var. sorediatus, C. foliosus, Cercocarpus betuloides, and C. montanus var. blanchae. Pedicularis densiflorus is the most common forb under the chaparral shrubs.

Central Coast Live Oak Riparian Forest (61220): 15 acres (6 ha). The survey was conducted in the second and third years of a drought; therefore, the stream conditions observed could be different from wetter years. This association type exists as mostly narrow corridors restricted in width by steep topography. The association is also found on some steep, north-facing slopes where shade and greater humidity help extend the community. Associated species include Quercus agrifolia, Q. chrysolepis, Q. wislizenii, Calochortus palmeri (CNPS List 1B), Arnica discoidea var. alata, Castilleja stenantha, Centaurium exaltatum, Delphinium nudicaule, Heterocodon rariflorum, Horkelia bolanderi, Leptodactylon californicum, Monardella macrantha, Populus fremontii, P. trichocarpa, Psoralea orbicularis, and Zigadenus venenosus.

Valley Needlegrass Grassland (42110): 12 acres (5 ha). This association type is restricted to small potreros that are mostly less than 1 acre (0.4 ha). It does not entirely fit in this Holland type description, as the potreros are somewhat depauperate in native bunchgrasses. 

The potreros are located on old landslides, most lying in an east-central cluster between 2920 and 3000 ft (890-914 m). The largest one is near the stream at the bottom of trail P12/FS3. An additional potrero lies alongside the northwest ridge at 3480 ft (1061 m). Associated species include Calochortus sp., Clarkia speciosa, Sidalcea hickmanii, and Malacothamnus niveus (Jepson [Hickman 1993]: M. jonesii, CNPS List 4).

Blue Oak Woodland (71140): Less than 1.5 acres (0.6 ha). This association type is located in the far southeast tip of the study area, outside the RNA boundary. It is a small savanna-form stand of Quercus douglasii (blue oak). The stand occupies a gentle southeast-facing slope at 3560-3700 ft (1085-1128 m). The majority of the trees are mature, and a few appear quite old. Evidence of regeneration is apparent by the presence of young trees. Diversity within the community appears only moderate, and introduced grasses and forbs are noticeably mixed with natives. Calochortus simulans (CNPS List 4) is found here.

Plant Diversity

Two hundred thirty-nine species of vascular plants are listed.

Conflicting Impacts

Recreational use of the area is generally light, although evidence of target shooters and mountain bikers was observed on trail 16E01 defining the northern and eastern boundaries.