The Ellis Group is a Jurassic stratigraphic unit of the Western Canadian Sedimentary Basin that extends across Alberta, Saskatchewan, Montana, and Wyoming. Named for Fort Ellis, Montana, it was first described by A.C. Peale in 1893 from outcrops in Rocky Creek Canyon. Dating from the Bajocian to Oxfordian stages, it consists mainly of shale and sandstone deposited in marine and transitional environments. In the subsurface of southern Alberta and northern to central Montana, it is commonly about 80 metres thick but reaches 150 metres in southeastern Alberta near the Sweetgrass Arch. Regionally, it lies above the Rundle Group, beneath the Mannville Group, grades west into the Fernie Group, and east into the Vanguard and Shaunavon formations. Oil is produced from its Sawtooth Formation in southeastern Alberta.