The Trump administration announced a plan Thursday that could allow oil drilling on over three-quarters of the nation’s largest piece of unprotected wilderness, overhauling a 2013 plan that limited development on the Alaskan reserve.

The 23-million acre National Petroleum Reserve-Alaska, which is roughly the size of Indiana, has attracted relatively little public attention compared with the neighboring Arctic National Wildlife Refuge. But it ranks as one of the most ecologically valuable and promising oil prospects in the country.