In the San Joaquin Valley of California, land conversion for agricultural and urban uses has resulted in profound habitat loss and diminished biological diversity. However, the large-scale retirement (i.e., removal from irrigated agricultural production) of farmland in the western San Joaquin Valley presents an opportunity to restore native plant communities and wildlife habitat values. A key objective of the proposed restoration efforts was to utilize local seed sources to the extent possible. However, local genotypes of San Joaquin Valley native plants are largely unavailable from commercial seed suppliers, and the amount of seed that could be collected from areas of native habitat would be insufficient for reseeding large tracts of retired farmland. Accordingly, we initiated a regional search for local native plant populations from which seeds could be collected and planted in a field nursery for the purpose of seed production. We identified 41 areas of remnant native habitat (sites) that supported 158 native plant species. The majority of the populations were restricted to isolated habitat remnants. Many of the species were uncommon: 65% were documented at three or fewer sites. The number of species per site was generally low; over half of the sites supported 10 or fewer species. This investigation illustrates the difficulty of identifying local native seed sources for restoration purposes in a highly fragmented landscape.