Public land grazing elicits some pretty damning declarations. Former Secretary of the Interior Bruce Babbitt once called livestock grazing “the most damaging use of public lands.” And conservation groups, like WildEarth Guardians, go further: “Livestock production is the most widespread and destructive activity on . . . western landscapes.”

And yet, little is known about permit holders authorized to graze sheep, cattle, goats, and horses on millions of acres of federal public lands in 16 states.

WildEarth Guardians, based in Sante Fe, N.M., is embroiled in a protracted legal battle to obtain the names of permit holders from the Interior Department ...