The rare Arctostaphylos glandulosa ssp. crassifolia is federally listed as an endangered species in the United States. There are about 25 remaining populations, most occurring in fragmented and degraded coastal sage scrub chaparral habitats on both sides of the border. Arctostaphylos glandulosa ssp. crassifolia is only known in the wild from one population near the Mill Creek Summit divide within the Angeles National Forest in the San Gabriel Mountains, and is on the California Native Plant Society Rare and Endangered Plant Inventory.