Contra Costa Goldfields

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Contra Costa Goldfields

Lasthenia conjugens

ListedJune 18, 1997
FamilyCompositae (Asteraceae)
DescriptionShowy spring annual, usually branched, with light green leaves and yellow flower heads.
HabitatVernal pools.
ThreatsLoss of habitat.


Lasthenia conjugens (Contra Costa goldfields), is a showy spring annual in the aster family (Asteraceae or Compositae) that grows 10-12 in (25-30 cm) tall and is usually branched. The leaves are opposite, light green, and usually have a feather-like arrangement with narrow clefts extending more than halfway toward the stem. The flowers are found in terminal yellow heads. The phyllaries are one-third to one-half fused; the achenes are less than 0.06 in (1.5 mm) long and always lack a pappus. Contra Costa goldfields flowers from March to June. The partially fused phyllaries and the lack of a pappus distinguish this species from L. fremontii and L. burkei, which it otherwise closely resembles.

Contra Costa goldfields was described in 1888 from specimens collected near Antioch in Contra Costa County, California. This taxon was included within Baeria fremontii in 1914; however, Ferris later recognized this material in 1958 as B. fremontii var. conjugens. In 1966, R. Ornduff submerged the genus Baeria under Lasthenia and recognized the specific rank of L. conjugens.


Habitat for Contra Costa goldfields consists of vernal pools in open grassy areas of woodland and valley grassland communities. Vernal pools are a natural habitat type of the Mediterranean climate region of the Pacific coast and the Central Valley of California. Covered by shallow water for extended periods during the cool season but completely dry for most of the warm season drought, vernal pools hold water long enough to allow some purely aquatic organisms to grow and reproduce, but not long enough to permit the development of a typical pond or marsh ecosystem. The alternation of very wet and very dry conditions creates an unusual ecological situation that supports a unique biota.


L. conjugens historically grew in vernal pool habitats in the California counties of Alameda, Contra Costa, Mendocino, Santa Barbara, Santa Clara, Napa, and Solano. The species is now known from a total of 13 populations in Alameda, Contra Costa, Napa, and Solano Counties. Eight of these populations were discovered after publication of the proposed rule and are located within the original range of the species near Fairfield in Solano County, and near Fremont in Alameda County. One population of L. conjugens occurs in Contra Costa County, two in Napa County, one in Alameda County, and nine in Solano County. Of the nine populations located in Solano County, eight are clustered near the town of Fairfield and one is located at Travis Air Force Base. All populations except the one located at Travis Air Force Base are on private lands.


Contra Costa goldfields is endangered because of the vulnerability of its restricted habitat to threats posed by urbanization, agricultural land conversion, drainage, vernal pool and pond construction, ditch construction, off-highway vehicle use, road maintenance, and random natural events.

L. conjugens is no longer found at its historical occurrences in Mendocino, Santa Clara, and Santa Barbara Counties. Agricultural land conversion, urbanization, and associated developments have extirpated populations of this species in Alameda, Contra Costa, Santa Clara, and Santa Barbara Counties. Agricultural land conversion extirpated one additional population of L. conjugens in Napa County. The widening and straightening of Ledgewood Creek north of Cordelia Road in Solano County by the U.S. Army Corps of Engineers both eliminated a large number of these plant individuals and destroyed a considerable amount of its habitat.

The largest known concentration of Contra Costa goldfields populations occurs in Solano County near the city of Fairfield. The General Plan for the city of Fairfield indicates that all of these populations are found in areas that will eventually be included within the Fairfield urban boundary. The implementation of this plan would result in the conversion of approximately 9,668 acres (4,000 hectares) of existing habitat and open space to urban use by 2020. This would include approximately 3,400 acres (1,375 hectares) within the Travis/ Northeast growth center where the greatest concentrations of Contra Costa goldfields occur. Two proposed residential development projects threaten the three largest populations of Contra Costa goldfields, which contain over 70% of all individual plants of this species. One of these populations is also threatened by landfill construction activities. This population may also be threatened by a ditch construction project proposed by the California Department of Water Resources.

Urbanization threatens the largest population of Contra Costa goldfields in Napa County. Off-highway vehicle traffic has also damaged this same population. In Contra Costa County, the primary transportation corridor, State Route 4, will be relocated to within approximately 80-100 ft (24-30 m) from the only remaining population in the county. Six of the eight newly discovered populations of Contra Costa goldfields in Solano and Alameda Counties are imminently threatened by development projects.

Livestock grazing threatens four populations of Contra Costa goldfields. The single extant occurrence of this taxon in Napa County occurs in a grazed field. Cattle-induced nutrient enrichment of vernal pool habitat has led to algal blooms and possibly other biotic changes in these pools that affect the growth of Contra Costa goldfields.

Conservation and Recovery

Only one of the 13 known populations of the Contra Costa goldfields occurs in habitat located on federally owned land. This habitat, in Travis Air Force Base, should be strictly protected from any development-related or other disturbances. The other habitats are all on privately owned land, and are threatened by destruction by residential or agricultural developments and by other disturbances. The largest critical habitats should be protected. This could be done by acquiring habitats and designating ecological reserves, or by negotiating conservation easements with the private landowners. The populations of the Contra Costa goldfields should be monitored, and research undertaken into its biology and ecological needs.


U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Building
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121

U. S. Fish and Wildlife Service
Sacramento Fish and Wildlife Office
Federal Building
2800 Cottage Way, Room W-2605
Sacramento, California 95825-1846
Telephone: (916) 414-6600
Fax: (916) 460-4619


U.S. Fish and Wildlife Service. 18 June 1997. "Endangered and Threatened Wildlife and Plants; Endangered Status for Four Plants from Vernal Pools and Mesic Areas in Northern California." Federal Register 62(117):33029-33038.