The Haynesville Shale is a deeply buried late Jurassic rock unit beneath northwest Louisiana, East Texas, and southwestern Arkansas, known both as an organic-rich part of the Haynesville Formation and as a major U.S. shale gas province. Formed about 151 to 157 million years ago in a restricted marine basin with oxygen-poor bottom waters, it preserved abundant organic matter in mudstones now found 10,500 to 13,000 feet underground. Though long known to contain large natural gas resources, it became economically important only after 2008, when hydraulic fracturing, directional drilling, and higher gas prices sparked a boom that brought major production and significant economic and social change, especially around Shreveport.