1993 – The Center petitioned the U.S. Fish and Wildlife Service to list the Huachuca water umbel as endangered under the Endangered Species Act.
January 1, 1996 – The Center filed suit against the Service for failing to list five riparian species, including the Huachuca water umbel.
January 6, 1997 – The Service listed the Huachuca water umbel as endangered, but designated no critical habitat for the species.
November 1997 – The Center filed suit against the National Forest Service, challenging 92 grazing allotments on seven national forests in the Gila and Little Colorado river basins, including allotments that would adversely affect the Huachuca water umbel.
November 3, 1997 – The Center filed suit against the U.S. Fish and Wildlife Service for failing to designate critical habitat for the plant.
1998 – The Forest Service admitted that 80 out of 92 grazing allotments could harm endangered species, including the Huachuca water umbel. It then announced it would publish an Environmental Impact Statement addressing the effects of grazing on endangered species within the bioregion of the allotments. The statement codified a plan to ban cattle from the habitats of eight species, but was very weak on protections for four others. It completely ignored the needs of the Huachuca water umbel and eight similarly imperiled plants and animals.
July 12, 1999 – In response to a federal court order, the U.S. Fish and Wildlife Service designated almost 52 miles of river as critical habitat for the Huachuca water umbel.
2000 – The U.S. Forest Service agreed to re-assess the impact of livestock grazing on 17 allotments in the Gila Basin.
July 2001 – The Center served notice against the Army Corps of Engineers, the Environmental Protection Agency, the Federal Emergency Management Agency, and others to prevent the expansion of Fort Huachuca without consideration of the effect on the San Pedro River and the endangered species that depend on it.
October 2001 – The Center and Forest Guardians filed suit challenging the continued grazing on 13,000 acres of public land in Arizona, which included habitat of the Huachuca water umbel and other endangered species.
2002 – A federal judge declared that Fort Huachuca's water conservation plan would not offset its expansion's impact on the Huachuca water umbel. The Fort was forced to develop a new plan.
February 2014 – The Center filed a cease-and-desist notice with the Federal Aviation Administration and Arizona's Department of Transportation to stop spending money for the construction of a new taxiway at the Sierra Vista Muni-Libby Airport. Initial work to support the taxiqway had already begun without an analysis of environmental harm, such as to the San Pedro River and its wildlife, including the Huachuca water umbel.