Navarretia fossalis

Known from southern California and adjacent Mexico, from northwestern Los Angeles County and western Riverside County south through coastal San Diego County to northwestern Baja California. In California, less than 20 occurences are believed extant and very few are presumed to remain in Mexico. Recent reporting on loss of populations is needed. Over half of known California occurrences are clustered at three general locations. This species' vernal pool habitats have been largely eliminated or severely disturbed in this region due to intensive conversion to agriculture and urbanization. The remaining habitat is subject to numerous threats, including ongoing agricultural or urban development, alteration of hydrology and floodplain dynamics, competition from non-native plants, road and pipeline construction, off-road vehicles, trampling by livestock, and weed abatement and fire suppression practices.

Known from southern California and adjacent Mexico, from northwestern Los Angeles County and western Riverside County south through coastal San Diego County to San Quentin in northwestern Baja California (USFWS 1998, 2005). A population was reported from San Luis Obispo County, California, but the identification of that population is believed to be in error (Spencer 2004 cited in USFWS 2005).

In California, less than 20 occurrences may be extant. As of 2010, ten occurrences are marked as extirpated (CNDDB 2010). Although there are 55 other occurrences in the CNDDB as of 2010, most of these have not been seen recently and a great deal of develoment has occurred in its habitat in the last 20 years. According to the U.S. Fish and Wildife Service (2005), over half of known California occurrences are clustered at three general locations: Otay Mesa (s. San Diego Co.), along San Jacinto River (w. Riverside Co.), and near Hemet (Riverside Co.). In Mexico, information from 1977 was that there were fewer than 10 populations, clustered in three general areas along the international border, on the plateaus south of the Rio Guadalupe, and on the San Quintin coastal plain (Moran 1977 cited in USFWS 2005). No more recent information is available but there are likely fewer occurrences in Mexico than there were in 1977.

This species is considered "seriously endangered" in California (CNPS 2009). Habitat destruction and fragmentation from urban and agricultural development is the greatest threat, followed by alteration of hydrology and floodplain dynamics (including excessive flooding and channelization) (USFWS 2005). Hydrological disruption may result from activities within occupied habitat and/or from more distant disturbances within the watershed. Competition from non-native plants also poses a threat at some locations; at some of these sites, active management of these plants is needed to maintain N. fossalis. Problematic plants include grasses such as Lolium multiflorum as well as forbs such as Brassica negra and Lythrum hyssopifolia. Other threats include road and pipeline construction, off-road vehicles, trampling by livestock, weed abatement and fire suppression practices (e.g. discing and plowing), illegal dumping, and foot traffic (USFWS 2005, CNPS 2009). Threats in Mexico unknown.