Astragalus cremnophylax is a rare species of milkvetch known by the common names sentry milkvetch and cliff milkvetch. It is endemic to Arizona, where the three varieties grow in three separate locations. The rarest variety, var. cremnophylax, is a federally listed endangered species which grows only on the rim of the Grand Canyon. The two other varieties are known from the Buckskin Mountains and Marble Canyon.