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Geologic-Neotectonic-Geomorphic Mapping Along the Santa Barbara-Ojai Coastal Strip

Mapping objectives: Neotectonic-geomorphic mapping will be conducted along the Santa Barbara-to-Ojai coastal strip to address landscape response to fault and fold geometry, kinematics, and displacement magnitudes and rates. This mapping will build on conventional geologic mapping that was conducted in the same area under the previous BALANCE and SCAMP projects to further characterize and understand the belt of active deformation and attendant landscape change and geohazards within and adjacent to the urbanized coastal lowlands. Conventional geologic mapping will be conducted in the western part of the Ojai 7½' quad to complete a Santa Barbara-to-Ojai coastal geologic map transect of the belt of young/active tectonic deformation and uplift. Also, conventional geologic mapping will be conducted in new exposures within burned areas of the 2009 "Jesusita" and 2008 "Tea" fires above the City of Santa Barbara to provide more detailed geologic substrate control for post-fire debris-flow monitoring efforts in the area. The latter mapping will also result in completion of the Santa Barbara 7½' quadrangle geologic map, the southern two-thirds of which was mapped earlier under SCAMP.

Topical objectives: (1) Develop a geologic and geomorphic framework for documenting and understanding the evolution of the Santa Barbara-Ojai fault and fold belt and the adjacent Santa Ynez Mountains range front. This objective task will provide a unified model concerning the Neogene tectonic history of, and landscape response to, a zone of active deformation and seismicity in the urbanized coastal environment. (2) Based on the geologic and geomorphic framework, provide constraints and input for models addressing the causes, probability, and location of range-front and coastal landsliding and erosion. (3) Complete detailed fault-kinematic studies initiated under BALANCE project along the Santa Barbara-to-Ojai fold-fault belt to decipher potential linkages between landform geomorphology and fault geometries and kinematics, and to provide constraints for seismic hazards models.

Highlights and Key Findings: Significant progress was made on mapping the geology of the southern flank of the Santa Ynez Mountains that was burned in the 2009 Tea and Jesusita fires. Improved exposures resulting from the fires on the steep mountain slopes revealed mass wasting features, deposits, and slope modifications that appear to be genetically linked to underlying bedrock lithology and structure.

In this view of part of the fire burn area on the Santa Ynez mountain flank above Santa Barbara, it is apparent that south dipping Eocene strata progressively steepen, become overturned, and break up into blocks upwards as they approach the ridge crest.  This pattern, which has been observed on several spurs descending the mountain front, suggests that down-slope creep and disaggregation of bedrock was a common process during and (or) following uplift of the mountain block.
In this view of part of the fire burn area on the Santa Ynez mountain flank above Santa Barbara, it is apparent that south dipping Eocene strata progressively steepen, become overturned, and break up into blocks upwards as they approach the ridge crest.  This pattern, which has been observed on several spurs descending the mountain front, suggests that down-slope creep and disaggregation of bedrock was a common process during and (or) following uplift of the mountain block.

Also identified as a result of the mapping is a previously unrecognized rangeward-dipping reverse fault having a trace length that likely exceeds 10 km.

Removal of dense chaparral brush as a result of the recent Gap and Jesusita fires on the mountain flank bordering the urbanized Santa Barbara coastal plain has exposed previously unrecognized faults and folds that may have helped accommodate Pleistocene uplift of the mountain block.  One such fault is highlighted in this photo by the narrow band of pale-gray rock that cuts across steeply dipping beds of Eocene strata.
Removal of dense chaparral brush as a result of the recent Gap and Jesusita fires on the mountain flank bordering the urbanized Santa Barbara coastal plain has exposed previously unrecognized faults and folds that may have helped accommodate Pleistocene uplift of the mountain block.  One such fault is highlighted in this photo by the narrow band of pale-gray rock that cuts across steeply dipping beds of Eocene strata.

This fault, which may have been active in the Quaternary, appears to have had a fundamental role in the overturning of strata during uplift of the Santa Ynez range front north of Santa Barbara.

   

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