Although it was described in 1878, Elaphrus viridis Horn (Carabidae) remained unknown for almost a century until its rediscovery during 1974 in the vernal pool-valley grassland region known as the Jepson Prairie in Solano County, California. Due to extensive loss and alteration of these seasonal wetlands and native grasslands throughout California's Central Valley, this beetle, commonly known as the Delta green ground beetle (DGGB), was recognized as a threatened species by the US Fish & Wildlife Service in 1980. However, despite its threatened species status, the beetle's geographic range, status, and habitat preferences have remained poorly known, factors that have hindered habitat management actions to benefit it. Presence-absence surveys were conducted throughout the entire approximately 200-km² Jepson Prairie region to document the DGGB's geographic range and identify its habitat associations and microhabitat preferences. Habitat relationships were investigated using a suite of biotic and abiotic features and discriminant function analyses to explain the beetle's geographic distribution throughout the region, its habitat associations, and preferred habitat structure. Initially, 36 habitat variables were measured at 240 randomly selected locations, with 60 locations in each of four actual or potential DGGB habitat types to characterize these habitats. These same habitat variables were also measured at 60 DGGB-occupied locations and used to determine the beetle's microhabitat preferences. Results of these field surveys and habitat analyses indicate that life stages of the DGGB prefer the sparsely vegetated habitats with short-statured vegetation where sunlight penetrates to ground level, along the gently-sloped shorelines of vernal playas underlain by Pescadero clay soils.