The mission of the BLM is "to sustain the health, diversity, and productivity of the public lands for the use and enjoyment of present and future generations." Originally BLM holdings were described as "land nobody wanted" because homesteaders had passed them by. All the same, ranchers hold nearly 18,000 permits and leases for livestock grazing on 155 million acres (630,000 km2) of BLM public lands. The agency manages 221 wilderness areas, 23 national monuments and some 636 other protected areas as part of the National Landscape Conservation System totaling about 30 million acres (120,000 km2). There are more than 63,000 oil and gas wells on BLM public lands. Total energy leases generated approximately $5.4 billion in 2013, an amount divided among the Treasury, the states, and Native Ameri