First Half of Field Trip
The 23rd Annual Fall Field Frolic
August 24 - 27, 2005
Field Trip Leaders:
Doug Yule, Jorge Vazquez, Dave Liggett,
Photos and text by Dave Liggett
At our first two stops we talked about water and power resources. We looked at the zanja (shown here) near the University of Redlands. The zanja (ditch), dug by Native Americans about 1820, was the first development of water resources on the Santa Ana River. It was used for irrigation and as a water supply for the city of Redlands.
We drove past the Seven Oaks Dam and talked about its role in flood control. We also saw Mill Creek No. 1, the first commercial three-phase power generation plant in the U.S. (complete in 1893). At Mill Creek we talked about the various tectonic blocks of the San Bernardino Mountains, their uplift, distribution of rock types, as well as various fault strands on the San Andreas system, their possible offsets, and past configurations.
Our next stop was in the Mill Creek Formation where we spoke about the various facies, their provenance, and the palinspastic reconstruction of the faults in
At the mouth of Mill Creek Canyon we looked at the gray breccia
facies. Jorge Vazquez described the distribution of the Pelona Schist
in southern California and various models for its origin.
Next we looked at the green sandstone and shale facies in the Yucaipa Ridge
syncline. Gene Fritsche described some of its sedimentary features.
Doug Yule explained that Yucaipa Ridge is bounded on the north by the Mill Creek
fault and on the south by the San Bernardino strand of the San Andreas fault.
The ridge is being squeezed between these two faults and has been uplifted at a very rapid rate.
Our last stop of the day was on the southern edge of the San Gorgonio massif
where we looked at
the megaporpryry of Manzanita Springs. This
rock has a counterpart 160 km to the west at Liebre Mountain. The
provides an important constraint in various reconstruction models of the San Andreas fault
We started day two with an overview of the geology of the San Bernardino
Mountains. Dave Liggett talked about glaciation, the Cenozoic Santa
Ana Formation, and landslide features in and around Barton Flats. Doug
Yule spoke about faults within and near the range and how they relate to the
overall regional tectonics scheme that has produced the San Bernardino Mountains.
We made stops to look at old and young debris flow deposits at Hathaway Creek
and Pelona Schist clasts in the Santa Ana Formation at Jenks Lake. Then we
headed up Lightning Gulch road to look at the Proterozoic-Paleozoic Big Bear Group
siliciclatic rocks. This photo shows the basal contact of the Big Bear
Group rocks that unconformably overly the Baldwin Gneiss basement. This
contact marks a billion year gap between the ages of these two units.
We hiked up the side of Sugarloaf Mountain through the lower members of the Big
Bear Group. This photo was taken in the Lightning Gulch Formation.
Go to the second half of the field trip
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