This species is restricted to habitats bordering San Francisco Bay in California in the United States. Occurrence within this small range is highly fragmented. The range encompasses salt marshes of the San Francisco Bay system (San Francisco, San Pablo, and Suisun bays), in central California (Shellhammer 1982). Subspecies halicoetes occurs in marshes of San Pablo and Suisun bays (and including Petaluma Marsh in Sonoma County) and along the northern Contra Costa County coast (east to Antioch dunes area), and subspecies raviventris occurs mostly in the southern part of South San Francisco Bay, with a few populations on the Marin Peninsula (west to the mouth of Gallinas Creek) and near Point Richmond (Shellhammer 1989). The remaining tidal marsh habitat in the San Francisco Bay Area is estimated to be 12,555 ha (=125 sq km). An unknown fraction of this habitat is actually occupied by this species.