Western Trilobites Association


Arranged by Geologic Time Period

List of Trilobite Formations Sorted by Geological Time:




Addy Quartzite (WA)

Brigham Quartzite (UT)

Bright Angel Shale (NV, AZ)

Burgess Shale Formation (B.C.)

Cadiz  Formation (California)

Campito Formation (California, NV)

Carrara Formation (California)

Cathedral Formation (Alberta, B. C.)

Chambless Limestone (California)

Chisholm Shale (NV, UT)

Damnation Limestone (Mont.)

Dome Limestone (UT)

Dunderberg Shale (NV)
Eager Formation (B.C.)

Emigrant Formation (NV)

Gordon Shale (Mont.)

Glossopleura Biozone (WA)

Harkless Formation (California, NV)

Langston Formation (Lead Bell Shale Member, Spence Shale Tongue) (UT)

Latham Shale (California)

Lead Bell Shale Member (Idaho) (see Spence Shale)

Marjum Formation (UT)
Meagher Shale (Montana)
Metaline Limestone (Washington)

McKay Group (B.C.)

Monola Formation (California)

Mount Whyte Formation (B.C., Alberta)

Mule Spring Limestone (California, NV)

Mural Formation (Alberta, B.C.)

Naiset Formation (Alberta, B.C.)

Naomi Peak Limestone (UT)

Pagoda Limestone (Mont.)

Peerless Formation (Colorado)

Pentagon Shale (Mont.)

Peyto Formation (Alberta, B.C.)

Pierson Cove Formation (UT)

Pika Formation (Alberta, B.C.)

Pioche Shale (NV)

Poleta Formation (California, NV)

Ptarmigan Formation (Alberta, B. C.)

Ross Lake Shale Member (Alberta, B. C.)

Saline Valley Formation (California, NV)

Spence Shale (UT, Idaho)

Steamboat Limestone (Mont.)

Stephen Formation (Alberta, B. C.)

Survey Peak Formation (Alberta)

Swazey Limestone (UT)

Takakkaw Tongue Formation (B.C.)

Twin Knobs Formation (Idaho)

Ute Limestone (UT)

Weeks Formation (UT)

Wheeler Shale (UT)

Whirlwind Formation (UT)

White-Inyo Mountains Biozones (California)

Wolsey Shale (Mont.)

Wood Canyon  Formation (California)

Zabriskie Quartzite (California)





Antelope Valley Limestone (NV)

Filmore Formation (UT)

Garden City Formation (UT, Idaho)

Manitou Formation (Colorado

Ninemile Shale (NV)

Outram Formation (Alberta)

Pogonip Group - Fillmore Formation (UT, CA)

Skoki Formation (Alberta)

Survey Peak Formation (Alberta)

Swan Peak Formation (UT, Idaho)

Wah Wah Formation (UT)





Gazelle Formation (CA)

Tegert Formation (B.C.)





Chaffee Formation, Dyer Dolomite Member (Colorado)

Haragan Formation (Oklahoma)
Kennett Formation (CA)
Williams Canyon Formation (Colorado)  




Baird Formation (CA)

Caballero Formation (N.M.)

Lake Valley Formation (Dona Ana, Arcente, Tierra Blanca, Nunn, Alamogordo, and Andrecito Members) (N.M.)

Kelly Formation (N.M.)

Ouray Limestone (Colorado)

Williams Canyon Formation (Colorado)





Beldon Formation  (Colorado)

Glen Eerie Formation (Colorado)

Hermosa Formation (Colorado)

Maroon Formation (Colorado)

Minturn Formation (Colorado)

Mount Mark Formation (B. C.)

Weber Formation (Colorado)





San Andreas Formation (N.M.)


Plea: Many of the faunal lists for these formations are incomplete or may have outdated generic assessments. Please point out any errors in synonomy or generic designations, as well as any additions or corrections to the faunal lists. This is a growing site and we look forward to any contributions of faunal lists or trilobite photos.