Astragalus microcymbus (Fabaceae) is a rare forb endemic to Gunnison County, Colorado. For 17 years, Denver Botanic Gardens and the U.S. Bureau of Land Management (Colorado State Office) have monitored four populations of this candidate species under the ESA in the South Beaver Creek Natural Area. Large, statistically significant population declines have been documented, as have prolonged dormancy, episodic fruit production, and herbivory. This study was initiated to learn about the life history of this rare species, determine the population trends, and examine management actions that will best support long-term survival of this species. Results indicate that while Astragalus microcymbus is declining in overall population size, it is following a large time scale cyclical pattern of growth and decline. Additional study is needed to fully understand the mechanisms driving mast seeding, prolonged dormancy, and population trends in this rare species.