DEB HAALAND, Joe Biden’s interior secretary, will lace up her hiking boots for a visit to Utah’s canyon country this week. Spectacular scenery aside, the trip is all business. Just hours after taking the oath of office on January 20th, Mr Biden directed his Interior Department to review Donald Trump’s changes to America’s national monuments with an eye to reversing them. Ms Haaland’s meetings with local officials on April 8th are a part of that review. Mr Trump’s decision in 2017 to dramatically shrink the Bears Ears and Grand Staircase-Escalante monuments in southern Utah amounted to the biggest reduction of federal land protections in American history. The rollback cheered conservative lawmakers from western states who are ideologically opposed to the idea that edicts from the White House can dictate how land some 2,000 miles away is used. The presidential power to declare national monuments is set out in the Antiquities Act, a little-known law passed by Congress in 1906. What does the law do and why is it so controversial?

In the late 19th century museums and fairs, such as the World’s Columbian Exposition, held in Chicago in 1893, began increasingly to display Native American artefacts. This exposure and the rise of American archaeological studies led to a surge in demand for antiquities from the country’s western states. Looting, vandalism and grave-robbing became common. Historic sites—especially around the Four Corners region where Colorado, Utah, Arizona and New Mexico meet—were plundered, sometimes by archaeologists themselves. In response, Congress passed the Antiquities Act, which gave the president the discretion to declare “historic landmarks, historic and prehistoric structures, and other objects of historic or scientific interest that are situated on land owned or controlled by the federal government to be national monuments”. In practice that means any new extractive activities are banned, including drilling, mining, logging and grazing. In modern times, monument designations may also limit the use of off-road vehicles.

The vagueness of the act’s wording made it a powerful tool for environmental conservation. Theodore Roosevelt, who signed the bill into law, made immediate use of his new executive power. An avowed conservationist, he created 18 national monuments—as well as 150 national forests and five national parks—during his tenure in the White House. Roosevelt’s successors followed suit. Every president since except Richard Nixon, Ronald Reagan and George H.W. Bush declared or enlarged national monuments (see chart). After gutting Bears Ears and Grand Staircase, Mr Trump protected 380 acres in Kentucky that had served as a training ground for African-American troops during the civil war.

The law has long been controversial, hardening battle lines between the legislative and executive branches, federal and state governments, tribes, scientists and industry. Individual states viewed it as a land grab by the feds; tribes were often not consulted when monuments were declared, enlarged or diminished; miners, ranchers, loggers and oilmen complained that the protections were bad for business. Liberty-loving Wyomingites objected so much to the practice that in 1950 a section was added barring the “extension or establishment of national monuments” in the state unless authorised by Congress. Mike Lee, Utah’s senior senator, is also pushing for an exemption for his state.

These competing interests still define the debate around America’s public lands. But even among westerners, national monuments are popular. A recent Colorado College poll found that 74% of Utahns support restoring protections for them. That is good news for the Biden administration, which hopes to protect 30% of American lands and waters by 2030. As of 2018 only 12% of the country’s lands and 26% of its territorial waters were protected, according to the Centre for American Progress, a think-tank. Declaring and enlarging national monuments will help Mr Biden meet that goal. Conservation by executive fiat has its drawbacks, however, in that it may be undone by future presidents. The tug-of-war over Bears Ears and Grand Staircase is proof of that precarity.