GEOLOGIC MAPPING AND DESCRIPTIONS OF PLIOCENE TUSCAN FORMATION LAHAR FLOWS, CHICO CALIFORNIA

New mapping and correlations of the Pliocene Tuscan Formation lahar flows, in northern California have produced more detailed descriptions of the continuity, flow characteristics, and lithologic variations of individual flow units. The field area is a 3.5 mile section of the Big Chico Creek Canyon, east of Chico, California in Butte County. Regionally, this area lies on the southwest flank of the Cascade Range Province, on the southwest boundary of the Chico Monocline. Photo-geology of the area produced initial correlations of individual flow units. Flow units are continuous up to 800 m. Fieldwork, along with several stratigraphic columns across the length of the field area, are used to validate the initial interpretations from photo-geology and describe variations of the clasts and matrix lithologies within flows. Preliminary work to correlate the flows across Big Chico Creek Canyon is useful for better understanding structural deformation of the flows, likely related to the construction of the Chico Monocline. This work and more detailed descriptions of individual flow units of the Tuscan Formation will be used to gain further insight into the nature of the source area, the Yana Volcanic Center, south of the Lassen Volcanic Center.