Named as one of four formations of the Upper Jurassic Cotton Valley Group in LA. Name applied to a dark-gray shale wedge that lies between Terryville Sandstone (new) of Cotton Valley and the Knowles Limestone (new) of Cotton Valley. Named for the Hico Field and town of Hico, Lincoln Parish, LA in the Arkla basin. Type section designated as between 8,130 and 9,330 ft in the Southwest Gas Producing Co., J. H. Peterson No. 1-V-10 in NE NE sec 25, T20N, R4W. Known only in the subsurface. Cross sections. Consists mainly of dark-gray shale but includes thin lenses of siltstone, shaly sandstone, and argillaceous limestone. Five sandstone tongues of the Terryville, its downdip equivalent, pinch out into Hico. Grades northward into the Schuler Formation of the Cotton Valley. Deposited in a lagoon. [Authors do not identify the nomenclature that was applied to these rocks in papers published prior to 1964.]

Source: GNU records (USGS DDS-6; Denver GNULEX).