Astragalus tricarinatus A.Gray (triple-ribbed milkvetch) is a rare perennial herb endemic to southern California and is listed as endangered under the Federal Endangered Species Act. Field surveys conducted between 2014 and 2017 relocated A. tricarinatus at one of three historical occurrences in the southern portion of its range in Riverside County, California. Surveys in the Chuckwalla Mountains and Orocopia Mountains were not successful in relocating historical occurrences; however, new occurrences were documented in the Santa Rosa Mountains. Plants in the Santa Rosa Mountains were growing on carbonate soils, a substrate that had not been previously associated with A. tricarinatus, which typically occurs on metamorphic rock of granitic origin.