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Soil Investigations for Data Collection in the Delta Initial Study/Proposed Mitigated Negative Declaration 115 However, this species has low potential to occur within the Study Area because the Study Area is located on the edge of its known range. Implementation of Mitigation Measures MM BIO-1b, MM BIO-18, and MM BIO-19 would reduce potential impacts to Carquinez goldenbush to: Less than Significant with Mitigation Incorporated. Northern California black walnut (Juglans hindsii) Northern California black walnut has a CRPR of 1B.1 but is not listed under FESA or CESA. This species is a perennial deciduous tree in the walnut family, and it blooms from April to May (CNPS 2019). It is endemic to California but has been used widely as rootstock for the English walnut (J. regia) with which it readily hybridizes, as well as in horticultural plantings, and is considered naturalized throughout much of its present range. Its historic range includes the southern Inner North Coast Ranges, southern Sacramento Valley, northern San Joaquin Valley, and San Francisco Bay Area (CNPS 2019, Jepson Flora Project 2019), but only three, possibly four extant occurrences in Contra Costa, Sacramento, and Napa counties have been confirmed to occur prior to extensive European settlement of California, and only these have generally been accepted as indigenous. Only one of these occurrences is considered a viable population (Potter, et al. 2018). It is presumed extirpated from Sacramento, Solano, and Yolo counties. It typically grows in riparian forest and riparian woodland (CNPS 2019). The microhabitat for Northern California black walnut includes deep alluvial soil associated with creeks or streams (CDFW 2019). Threats to this species include hybridization with orchard trees, urbanization, and conversion to agriculture (CNPS 2019). This species has moderate potential to occur within the Study Area based on the presence of potentially suitable habitat. Implementation of Mitigation Measures MM BIO-1b, MM BIO-18, and MM BIO-19 would reduce potential impacts to Northern California black walnut to: Less than Significant with Mitigation Incorporated. Contra Costa goldfields (Lasthenia conjugens) Contra Costa goldfields is listed as Endangered under FESA and has a CRPR of 1B.1, but is not listed under CESA. This species is an annual herb in the sunflower family, and it blooms from March to June (CNPS 2019). It is endemic to California, and its current range includes the southern Sacramento Valley, Central Coast, and San Francisco Bay Area. It was formerly found in the North Coast, Outer North Coast Ranges, and South Coast (CNPS 2019, Jepson Flora Project 2019). It is presumed extirpated from Mendocino, Santa Barbara, and Santa Clara counties. It typically grows in cismontane woodland, playas, valley and foothill grassland, and vernal pools (CNPS 2019). The microhabitat for Contra Costa goldfields includes vernal pools, swales, and low depressions in open grassy areas (CDFW 2019). Threats to this species include development, habitat alteration, hydrological alterations, overgrazing, and non-native plants