It is the first "horse gather" in 13 years.
"Basically everything we are doing is new," Ken Sandusky, Forest Service spokesman, told the Bee. "The other option is long-term holding, which makes unlimited sale the only fiscally responsible option."
All of the horses will be made available for adoption. After 30 days, all horses 10 years and older, about 300 animals, will be made available for sale without limitations, the American Wild Horse Campaign, an animal rights group, said.
Although the U.S. Department of the Interior prohibits selling horses and burros under its supervision to slaughterhouses, the Forest Service, which falls under the U.S. Department of Agriculture, has no such restriction.
The government is exploiting a legal loophole, the animal rights group told the Bee.
"It's a sad irony that the first federally protected wild horses in decades to be purposefully sold by the government for slaughter will come from California — a state where the cruel practice of horse slaughter has been banned since the 1990's," Suzanne Roy, executive director of the horse campaign, said in a release.
The Associated Press contributed to this report.