Article
The Bear River’s diversion and the cutting of Oneida Narrows at ~55 ka and relations to Lake Bonneville Record
Utah Geologic Survey
(2019)
Abstract
The Bear River’s course has shifted over Quaternary time, and its late Pleistocene integration into the Bonneville basin long has
been recognized as a possible explanation for why Lake Bonneville was apparently larger than the preceding lakes in its basin,
and the only one to overflow its topographic threshold.
The middle-Pleistocene Bear River joined the Snake River to the north, likely via the Portneuf River drainage. Then an episode
of volcanism in the Blackfoot-Gem Valley volcanic field ~100–50 ka diverted the Bear River southward into Gem Valley. Previous
chronostratigraphic and isotopic work on the Main Canyon Formation in southern Gem Valley indicates internal-basin
sedimentation during most of the Quaternary, with a possible brief incursion of the Bear River ~140 ka. New evidence confirms
that the Bear River’s final diversion at ~55 ka led to its integration into the Bonneville basin by spill-over at a paleo-divide
above present-day Oneida Narrows dam. This drove rapid incision of 200 m of bedrock in the canyon and excavation of southern
Gem Valley in the subsequent millennia, before the rise of Lake Bonneville back flooded the area, as constrained by new
optically stimulated luminescence dates above, within, and below the canyon.
Bear River integration into the Bonneville basin early during marine isotope stage 3 seems to postdate the Cutler Dam lake
cycle, although that penultimate pluvial lake is incompletely dated and understood. It is also possible the Bear River’s hydrologic
addition relates to the recently recognized but poorly constrained Pilot Valley shoreline that predates the main Bonneville
lake cycle. Regardless, the Bear River certainly contributed to the rise of Lake Bonneville, culminating in the Bonneville flood.
Disciplines
Publication Date
2019
Citation Information
Pederson, J.L., Rittenour, T,M., Jänecke, S.U., Oaks., R.Q., Jr., 2019, The Bear River’s diversion and the cutting of Oneida Narrows at ~55 ka and relations to Lake Bonneville Record. In W.R. Lund, A.P. McKean, and S.D. Bowman (Eds.), Proceedings Volume: 2018 Lake Bonneville Geologic Conference and Short Course. Day 1, Sessions 1-4; Utah Geological Survey. Miscellaneous Publication, MP-170-1, p. 74-89. https://ugspub.nr.utah.gov/publications/misc_pubs/mp-170/mp-170-1.pdf