Bureau of Land Management officials say 647 "excess" mustangs were removed from the range in Humboldt and Pershing counties during the gather that ended Thursday.
They say the roundup was needed because of a lack of forage and water on the range due to the drought and the poor condition of horses.
Anne Novak of Protect Mustangs says the BLM should impose limits on mining and ranching if it wants to improve rangeland health. She says horses cost the American taxpayer nothing when they live in the wild.
Horses removed from the range by the BLM are put up for adoption or sent to government-funded pastures in the Midwest.