Gaining Insight into Butte Creek Canyon and its Geologic History Geos. 306 Jake Farhar
A Little Background Info • Chico Formation: Approx. 65-75 Ma, late Cretaceous. Generally a light to dark gray sandstone. Often found and identified by its numerous shells and shell fragments within the sandstone. (see photo*) • Lovejoy Basalt: Approx. ~15.4 Ma, Miocene. A hard, black, fine-grained rock, heavily fractured. Formed from very-fluid lava flows, individual flows are usually 10-30 feet thick. (see photo*) • Tuscan Formation: Approx. 2.8-3.3 Ma, late Pliocene. Consists of many layers of volcanic-mudflow debris a.k.a. lahars, also within the lahars are things it had picked up during its flow, creating; conglomerate, sandstone and siltstone, all with abundant particles of volcanic rock. (many photos in presentation)
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Results of Initial Survey • Found only Tuscan rock outcroppings • Noted: interesting alternating ash and conglomerate/breccia layers • Noted: possible correlation between younger layers and lighter colored clasts as rock layers get younger? • Made a friend: Jasper
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Results of Secondary Survey • Still no Lovejoy Basalt • Noted: more interesting ash layers • Found a possible cross-sectional fluid channel • Respect for field geologists went way up • Remember pants and a machete next survey
Interesting Strata Searching high and low on the slopes and cliff faces of the canyon so far, I have seen primarily the Tuscan Formation in all of its glory. However I have yet to find the fabled Lovejoy Basalt, which supposedly resides below it. (and certainly no Chico Formation which lies even below the Lovejoy) I had hoped to have much greater success on the alternate side of the canyon because of its taller and steeper cliffs. Sadly this wasn’t the case. However, that disappointment aside… I have seen many interesting stratagraphic structures and layers. Including cross-bedding, layering and possible folding of what appear to be almost exclusively ash flow deposits, of which I have multiple photos. (Generally ½’ to 6’ thick) The canyon is on a slope, the downward direction of the slope is in the approximate direction of West, Southwest, which means the canyon and all it contains, ie: the creek, the rock formations, the main-road, all are lower in elevation at the mouth/foot of the canyon than they are at the top. This means that I probably just didn’t go far/deep enough into the canyon to see where the Lovejoy actually starts to become visible in outcroppings.
References • Sullivan, April 2005, Paleographic Analysis of the Tuscan Formation, Chico, California, The Geological Society of America. http://gsa.confex.com/gsa/2005CD/finalprogram/abstract_85814.htm • Teasdale, Greene, Geology of the Big Chico Creek Ecological Preserve, Chico California, California State University Chico. • Garrison, N.J., Busby, C.J., Gans, P.B, Putirka, K, and Wagner, D.L., 2008 A mantle plume beneath California? The mid-Miocene Lovejoy flood basalt, northern California, in Wright, J.e., and Shervais, J.W., eds., Ophiolites, Arcs, and Batholiths: A Tribute to Cliff Hopson: Geological Society of America Special Paper 438.