San Bernardino Mountains

First Half of Field Trip

The 23rd Annual Fall Field Frolic

August 24 - 27, 2005

Field Trip Leaders:

Doug Yule, Jorge Vazquez, Dave Liggett,

First Half of Fall 2005 Dept Trip

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 the region. 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 megaporphyry provides an important constraint in various reconstruction models of the San Andreas fault system.
	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.
	We stopped to look at the 1.8 Ga Baldwin Gneiss. Jorge Vazquez spoke about possible source areas for this rock in the supercontinent Rodinia.
	On the last stop of day two we looked at this outcrop of 6.2 Ma vesicular olivine basalt in the Santa Ana Sandstone.

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THIS PAGE LAST MODIFIED SEPTEMBER 16, 2005