The Idaho Historical Society has erected a sign at this
location. There is an ample dirt parking lot. Concrete stairs
lead up a hill in the middle of the pass to provide a view of
the entire valley.
Lake Bonneville existed at various sizes from about 32,000 to
14,000 years ago. At is maximum Lake Bonneville covered much of
western Utah and extended across the borders with Idaho and Nevada
and reached a maximum depth of 1000 feet. At this location, Lake
Bonneville filled the valley to the south.
Outline of Lake Bonneville image:
Utah Geologic Survey, Lake Bonneville
(http://www.ugs.state.ut.us/online/PI-39/pi39pg01.htm)
During this time, the climate was wetter and colder than the
current climate. Lake Bonneville was a relatively fresh water lake
that was filled with rain water, rivers, streams, and melting
glaciers. For most of its history, Lake Bonneville was a terminal
lake because and had no natural outlet to the ocean.
However, about 50,000 years ago the Bear River was blocked from
draining into the Snake River and began draining into Lake
Bonneville. Prior diversions had occurred, but appear to have been
intermittent. This additional input of water began filling the lake
at a faster rate.
It continued filling until about 16,800 when it reached the
elevation of alluvial fans that had filled Red Rock Pass (This is a
different age than is on the sign because of the different
scientific references used). Red Rock Butte, the outcrops just
north of here were almost completely covered by the alluvial fans.
For about 500 years the flow out of the lake was controlled,
allowing the Bonneville shoreline to be etched into the
mountainsides all around the Salt Lake.
It is thought that the flow out of the lake began on the east
side of the pass and eroded down to the limestone bedrock. Erosion
began migrating westward into the unstable alluvial fan gravels
that covered the west side of the valley. At some point, the
outflow undercut the alluvial fan causing a 17 km2 landslide
initiating a catastrophic flood. Once the flood began, the water
rushed out eroding out about 375 feet of sediment and rock in less
than a year.
Maps from Link, 1999
Logging requirements:
Send me a note with :
- The text "GC15FH5 Red Rock Pass - Lake Bonneville Flood" on the
first line
- The number of people in your group.
- The current river that the flood flow is compared to and the
comparison
- If the mountains to the northeast were almost covered by the
alluvial fans, how far below ground would the coordinates be before
the flood (check TopoZone for the elevation of those
mountains.
- If you head north, look for the remnants of the alluvial fans
on the east or west side of the valley.
]I will only respond if you have incomplete
logging requirements. Go ahead and log your cache
The above information was compiled from the
following sources:
- Willis, Grant C. et al, Geology of Antelope
Island State Park, Utah in Geology of Utah's Parks and Monuments,
2003 Utah Geological Association Publication 28 (second edition)
D.A. Sprinkel, T.C. Chidsey, Jr. and P.B. Anderson,
editors
- Utah Geological Survy, Lake Bonneville, PI-39
Commonly Asked Questions About Utah's Great Salt Lake and Ancient
Lake Bonneville,
http://www.ugs.state.ut.us/online/PI-39/pi39pg01.htm
- Utah Geological Survey, Great Salt Lake,
http://www.ugs.state.ut.us/utahgeo/gsl/index.htm
- Link, Paul Karl, Darrell S. Kaufman and
Thackary, Glenn D. 1999; Field Guide to Pleistocene Lakes Thatcher
and Bonneville and the Bonneville Flood, Southeastern Idaho in
Hughes, S.S., and Thackray, G.D., eds., Guidebook to the Geology of
Eastern Idaho, Idaho Museum of Natural History.
- Bright, Robert C. and H. Thomas Ore, Evidence
for the spillover of Lake Bonneville, southeastern Idaho, in
Geological Society of America Centennial Field Guide, Rocky
Mountain Section, 1987.