A U.S. law from the pick-and-shovel days of the Western frontier now threatens natural treasures including Grand Canyon National Park as mining claims on public lands proliferate, an environmental group said on Friday.

The 1872 Mining Law, signed by President Ulysses S. Grant, allows mining companies — including foreign-owned ones — to take about $1 billion a year in gold and other metals from public lands without paying a royalty, according to a report by the nonprofit Pew Environment Group.

“The law was enacted … to encourage the development of the West and … rewarded those people who trekked across the frontier and gave them the right to mine gold, silver, whatever other valuable metals they could find on public land in unlimited amounts for free,” said Pew’s Jane Danowitz.