The final obstacle in the path of the muster was cleared last week, when US District Court Judge Paul Friedman refused a request for a preliminary injunction to stop the Bureau of Land Management (BLM) beginning the operation in the so-called Calico Complex, an area of 500,000 acres comprising five formal herd management areas.
Animals removed during the operation, which will take weeks, will be taken to Reno. They will either be adopted out or taken to longer-term holding facilities in the Midwest.
Several protests by wild horse advocates, who have called the muster inhumane and unnecessary, have been organised.
While the court action by the group, In Defense of Animals, ecologist Craig Downer, and children's author Teri Farley, failed to stop the muster, it did give the wild horse advocates scope for further action.
Judge Friedman said he saw merit in the advocate's legal argument around the ongoing placement of excess horses in long-term holding facilities in Oklahoma, Kansas and South Dakota.
Judge Friedman, in his 25-page decision, said the bureau's practice of holding tens of thousands of horses in long-term holding facilities in the Midwest, outside Nevada, did not appear to be authorised by law.
"The BLM's relocation of excess horses to those facilities for indefinite holding periods violates the plain language of Section 1339," the judge said.
"Furthermore, BLM's use of long-term holding facilities runs counter to the statute's mandate that the agency's management of wild horses occur at 'the minimal feasible level'.
"Long-term maintenance of thousands of horses in holding pens constitutes intensive management that was not contemplated by Congress when the Wild Horse Act was passed.
"... BLM's proposed confinement of hundreds or thousands of horses from the Calico Mountains Complex in long-term holding facilities in other states thus appears to contravene the unambiguous intent of Congress as expressed in statutory text and legislative history.
"It therefore is likely that the agency's interpretation of the statute as permitting such long-term holding and maintenance must be rejected ..."