Nortonville Coulter Pine Groves
Map SatelliteIn this area are found both the northernmost and some of the best stands of Coulter pine, Pinus coulteri, in the State. Gray pine, Pinus sabiniana, a closely related taxon, grows here also. The two pines form a distinct pine woodland association on several ridges in the area. Excellent examples of chaparral and oak woodland communities are also found here and there is some grassland.
Floristically, the area is very similar to the better known areas on Mount Diablo, a few kilometers southwest. The common manzanita, Arctostaphylos manzanita, reaches its southern limit in the Coast Ranges here, while the black sage, Salvia mellifera, is at its northernmost limit. Three rare plants are found in the area, Hesperolinon brewerii, Helianthella castanea, and Arctostaphylos auriculata, the latter being a narrow endemic known only from this region and Mount Diablo. This is also the only known site in the inner South Coast Ranges for the balsam root, Balsamorhiza deltoidea. The uncommon Dudleya setchellii is abundant on several of the steep canyon walls. Other plants of note found here include hop-tree, Ptelea crenulata, chaparral pea, Pickeringia montana, bush poppy, Dendromecon rigida, and Malacothamnus fremontii ssp. cercophorus. Approximately 200 species of vascular plants are found in the area.
Correlations between plant associations and geological formations are remarkably well illustrated here. The area is underlain by Domengine sands, which are steeply dipping and highly faulted, interspersed with layers of softer Nortonville shale. Both date to the Upper Eocene. There is a corresponding alternation between the areas of chaparral, which occupy the shallower, poorer soils formed by the ribs of sandstone, the pine groves, which are found on the deeper, sandy soils formed by the disintegration of the sandstone, and the oak woodland, which covers the areas of clay loam soil underlain by the shales and softer rocks. The heavier clay soils are covered by open grassland.
A typical inner Coast Range fauna is found here.
Integrity: The area has been grazed but this has not materially affected the area. It has also been mined for coal, heavily in the 1870 - 1900 period and last in the 1930's, as well as for silica sand for foundry use in the 1940's. A powerline crosses a corner of the area and there are various trails and roads. Some off-road vehicle damage is evident.
Use: Public areas: research, educational, observational, light recreational. Remainder, private.
Ref: Jenkins, O. P. (ed.) 1951. Geologic Guidebook of the San Francisco Bay Counties. Calif. Div. of Mines and Geol. Bull. 154, San Francisco, pp. 349-356.
January 1976
Inventory of California Natural Areas
Revision © 2009 Steven Louis Hartman
