Initial Publication Date: June 17, 2005

Upper Cretaceous-Paleocene Sequence, Bug Creek Area, Northeastern Montana

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Start point

no route given

End point

no route given


Montana 24, dirt road


The dirt road to the Bug Creek area is passable by any vehicle when dry; four-wheel drive is required in wet weather. Land is controlled by the Charles M. Russell National Wildlife Refuge and U.S. Bureau of Land Management. No permits are required except to collect vertebrate fossils.

Total distance

no route given



Study of the Late Cretaceous-Paleocene sequence in the Bug Creek Area and the rest of the Fort Peck Fossil Field has contributed greatly to our understanding of the paleoecology and stratigraphy of dinosaur extinction and the primary radiation of Tertiary placental mammals. The area features at least 133 species of spores and pollen, 93 species of Cretaceous vertebrates (including 30 species of mammals and 19 species of dinosaurs), 24 species of Paleocene mammals, as well as the oldest ungulate and primate specimens ever found. Fossil leaves and wood have also been described. The area also includes well-studied localities of the K/T boundary containing Ir-rich clay and shocked quartz. No section of terrestrial sediments across the K/T boundary has been studied in as many ways as this one. This has been and will continue to be a major locality at which to study evidence for various hypotheses about the events at the K/T boundary.

Key Lithologic Features

  • Bearpaw Shale (Cretaceous): marine shale
  • Fox Hills Sandstone (Cretaceous): marine and beach sandstones with interbedded shales
  • Hell Creek Formation (Cretaceous): sandstones, shales, siltstones, and charcoal deposits
  • Tullock Formation of the Fort Union Group (Paleocene): sandstones, siltstones, shales, coals



  • badlands topography

Other Features

  • diverse assemblage of vertebrate, plant, and trace fossils


Sloan, R.E., 1987, Upper Cretaceous-Paleocene sequence, Bug Creek area, northeastern Montana, in Beus, S.S., ed., Centennial Field Guide Volume 2: Rocky Mountain Section of the Geological Society of America , p. 45-48.


Out of print. Check Digital access to this publication is available via the links in the references section above.