https://www.usgs.gov/publications/lower-cody-shale-niobrara-equivalent-bighorn-basin-wyoming-and-montana-thickness
The lower shaly member of the Cody Shale in the Bighorn Basin, Wyoming and Montana is Coniacian to Santonian in age and is equivalent to the upper part of the...
cody shalein thebighorn basinlowerniobrara