The Drum mountains have a mixture of the Wheeler and Marjum formations in what is referred to by some as the Pierson Cove Formation. Parts of the Pierson Cove are referred to as "shallow Wheeler Formation" (Pierson Cove Formation), Millard County, Utah - Middle Cambrian, while most are more correctly referred to as Marjum.
Please refer to the Wheeler and Marjum
Formations for complete faunal lists.
See also the Gunther's site at http://www.geo-tools.com/003-03.htm for a more complete description.
DRUM MOUNTAINS, MILLARD CO., UTAH
Modocia sp. aff. M. laevinucha
According to the Sundberg paper, some of these trilobites (Altiocculus concavus & drumensis, Kootenia dawsoni, and Dorypyge swasii) are only in the Swasey Ls. and do not extend into the Wheeler. It is possible that the collectors digging there do not know where the boundary is between the Swasey Ls. and the Wheeler, and thus call it all Pierson Cove. It is however more likely due to researcher collection bias, where researcher tend to target beds that will produce abundant trilobite parts rather than seeking out complete trilobites within shale and mudstone units.
and compiled by James Cook, Andrew Milner and Kevin D. Brett