Bisti/De-Na-Zin Wilderness is south of Farmington, in San Juan County, New Mexico, USA. This fantasy world of strange rock formations is made of interbedded sandstone, shale, mudstone, coal, and silt. These rock layers have weathered into eerie hoodoos (pinnacles, spires, and cap rocks). This was once a riverine delta west of an ancient sea, the Western Interior Seaway, which covered much of New Mexico 70 million years ago. Swamps built up organic material which became beds of lignite. Water disappeared and left behind a 1400-foot (430 m) layer of jumbled sandstone, mudstone, shale, and coal. The ancient sedimentary deposits were uplifted with the rest of the Colorado Plateau, starting about 25 million years ago. Waters of the last ice age eroded the hoodoos now visible. The high desert widerness of Bisti is managed by the US Bureau of Land Management (BLM).