The Bear River's History and Diversion: Constraints, Unsolved Problems, and Implications for the Lake Bonneville Record

J. L. Pederson, S. U. Janecke, M. C. Reheis, D. S. Kaufman, R. Q. Oaks

Research output: Chapter in Book/Report/Conference proceedingChapter

5 Scopus citations


The shifting course of the Bear River has influenced the hydrologic balance of the Bonneville basin through time, including the magnitude of Lake Bonneville. This was first recognized by G.K. Gilbert and addressed in the early work of Robert Bright, who focused on the southeastern Idaho region of Gem Valley and Oneida Narrows. In this chapter, we summarize and evaluate existing knowledge from this region, present updated and new chronostratigraphic evidence for the Bear River's drainage history, and discuss implications for the Bonneville record as well as future research needs. The Bear River in Plio-Pleistocene time joined the Snake River to the north by following the present-day Portneuf or Blackfoot drainages, with it likely joining the Portneuf River by middle Pleistocene time. An episode of volcanism in the Blackfoot-Gem Valley volcanic field, sparsely dated to ~ 100–50 ka, diverted the Bear River southward from where the Alexander shield volcano obstructed the river's path into Gem Valley. Previous chronostratigraphic and isotopic work on the Main Canyon Formation in southern Gem Valley indicates internal-basin sedimentation during the Quaternary, with a possible brief incursion of the Bear River ~ 140 ka. New evidence confirms that the Bear River's final diversion at 60–50 ka led to its integration into the Bonneville basin by spillover at a paleo-divide above present-day Oneida Narrows. This drove rapid incision before the rise of Lake Bonneville into the canyon and southern Gem Valley. Bear River diversion at 60–50 ka coincides with the end of the Cutler Dam lake cycle, at the onset of marine isotope stage 3. The Bear River subsequently contributed to the rise of Lake Bonneville, the highest pluvial lake known in the basin, culminating in the Bonneville flood. Key research questions include the prior path of the upper Bear River, dating and understanding the complex geologic relations within the Gem Valley-Blackfoot volcanic field, resolving evidence for possible earlier incursions of Bear River water into the Bonneville basin, and interpreting the sedimentology of the Main Canyon Formation.

Original languageEnglish (US)
Title of host publicationLake Bonneville
Subtitle of host publicationA Scientific Update, 2016
EditorsCharles G. Oviatt, John F. Shroder
PublisherElsevier B.V.
Number of pages32
ISBN (Print)9780444635907
StatePublished - 2016

Publication series

NameDevelopments in Earth Surface Processes
ISSN (Print)0928-2025


  • Bear River
  • Drainage integration
  • Gem Valley
  • Lake Bonneville
  • Paleohydrology

ASJC Scopus subject areas

  • Global and Planetary Change
  • Geology
  • Earth-Surface Processes
  • Atmospheric Science


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