June 16, 1987 – The Sacramento Mountains thistle was listed as threatened under the U.S. Endangered Species Act.
April 30, 2004 – The Otero County Board of Commissioners petitioned to delist the thistle.
December 5, 2006 – The U.S. Fish and Wildlife Service rejected the Board's petition.
August 31, 2007 – The Board of Commissioners again petitioned to delist the thistle.
December 9, 2008 – The Center submitted formal comments on the thistle's endangerment to keep the plant protected.
June 2, 2010 – The Fish and Wildlife Service again rejected the petitioners' request for delisting, agreeing with the Center that the Sacramento Mountains thistle still needs federal protection.