April 20, 1999 – The U.S. Fish and Wildlife Service listed the Sierra Nevada bighorn sheep as endangered under the Endangered Species Act on an emergency basis.
January 3, 2000 – The Service found that the Sierra Nevada bighorn constituted a distinct population segment and published a final rule listing the species as endangered on a permanent basis.
December 8, 2005 – The Center sued the Service for its failure to designate critical habitat for the sheep.
July 25, 2007 – The Service proposed designating 417,577 acres of critical habitat for the bighorn sheep. A final decision was due on July 17, 2008.
September 24, 2007 – The Service published a recovery plan for the sheep.
February 2008 – The Service announced the publication of a recovery plan for the Sierra Nevada bighorn sheep. The agency also announced the availability of the draft economic analysis for the species' critical habitat designation and reopened the critical habitat comment period until March 6, 2008.
August 5, 2008 – The Service designated more than 400,000 acres of land as critical habitat essential for the sheep's survival and recovery in the eastern Sierra Nevada.
September 9, 2008 – A coalition of conservation groups, including the Center, filed suit against the Bush administration over weak forest-management plans that threaten wildlife in 10 Sierra Nevada national forests, including Sierra Nevada bighorn sheep.
April 15, 2009 – The Center and Public Employees for Responsibility notified the Forest Service and Bureau of Land Management that we'd sue if they did not take steps to protect the Sierra Nevada bighorn from disease transmitted from domestic sheep on sheep allotments in Mono County.
June 2009 – The Center and more than 13,700 of our supporters weighed in on BLM proposals to restrict grazing at the Green and Dog Creek allotments.
October 2014 – The BLM's long-delayed decision on the Green and Dog Creek allotments eliminated domestic sheep grazing (although it still allows some use for tailing sheep bands across the allotments to private lands).
December 2016 – Mono County began consideration of a domestic sheep–grazing lease renewal on county-owned Conway and Mattly ranches, where grazing would pose a high risk of disease transmission to Sierra Nevada bighorn sheep. The Center had asked the county to ensure full consideration of risks to bighorn before any approvals to protect conservation values.
February 2017 – The Fish and Wildlife Service sent a letter to Mono County urging the county to eliminate domestic sheep grazing on Conway and Mattly ranches to protect Sierra Nevada bighorn populations nearby.