Outside Taos, N.M., there's an 800-foot rift in the earth, 50 miles long. The gorge bores through a vast volcanic field, a plateau where elk, mule deer, pronghorn, and sheep winter. For 10,000 years or more, humans have gathered here, evident by petroglyphs of game carved into boulders along the Rio Grande, at the bottom of the canyon. In 2013, President Barack Obama designated this land as the Rio Grande del Norte National Monument, owing to its archaeological and scientific significance. Two weeks ago, I had a chance to fish and float through the monument, and it was staggering, both for its abundance of wildlife and for its raw, wild beauty. At 243,000 acres, it is one of the nation's largest monuments, and it's also one of the 27 currently under review by the Department of the Interior, acting on orders from President Donald Trump. The review is intended to determine whether the monuments meet the requirements and original objectives of the Antiquities Act, the law under which they were created. The review has sparked criticism from conservation and sportsmen's groups, for its outcome could radically affect public-land usage in this country, and unlikely for the better. But why would the Trump Administration want to review, and likely reduce the size of, national monuments in the first place? Why have these lands come under attack?