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Basins & Landscape Co-Evolution in Southern California
Project Chief: Jonathan Matti
Funded by the National Cooperative Geologic Mapping Program (FEDMap)

Statement of Problem: In southern California, interaction among climatic and tectonic factors has created a dynamic framework within which degradational and aggradational processes have shaped Neogene landscapes.   The southern California landscape comprises three co-evolving groups of landforms:   (1) Mountain ranges.—Carved from uplifted blocks of crystalline basement rocks or from blocks of tilted sedimentary strata, highlands exhibit erosional landscapes sculpted by surficial processes. Landforms include sequences of geomorphic surfaces, some of which are old and pass beneath adjoining basins, some of which have developed contemporaneously with the basins.   (2) Lowland valleys.—Basins beneath lowlands have been filled by Late Cenozoic sequence-stratigraphic packages of sediment derived from adjacent highlands. Some degradational surfaces between basinal sedimentary packages correlate with surfaces on adjacent highlands.   (3) Mountain fronts.—Range fronts in southern California typically are steep, are active geomorphically and tectonically, and form dynamic boundaries between basins and highlands. Understanding how range fronts evolve, segment, migrate, and cannibalize adjoining basins is a key factor in understanding landscape evolution.   These three physiographic elements record distinct but complementary records of landscape evolution that should be investigated as an integrated system. It is especially important to use geologic, geomorphic, and geophysical mapping to document relations among landform evolution, bedrock substrate, and surficial deposits. Based on this mapping, project members are conducting systematic investigations of how geologic substrate, tectonic history, and climatic conditions combine to influence landscape evolution at local and regional scales. Our findings will provide insight into tectonic processes and rates for the late Cenozoic leading up to the late Holocene——the focus of paleoseismic and seismic studies evaluating earthquake risk in the southern San Andreas Fault system.

Objectives:  Develop a regional geologic/geomorphic/geochronologic framework for evaluating and synthesizing late Cenozoic landscape evolution in southern California. This overall objective has several components:   (1) Using geologic and geomorphic mapping, document the distribution of major degradational and aggradational surfaces in selected parts of southern California, keyed to tectono-geomorphic domains associated with the San Andreas Fault;   (2) Establish the relative chronology of degradational surfaces on basement highlands, and determine analytical ages for their development;   (3) Clarify the stratigraphic framework and evolution of relevant late Cenozoic sedimentary basins and sequences and associate them with specific highland surfaces; some of these basins and highlands have been displaced along the San Andreas Fault zone and need to be palinspastically re-associated;   (4) Integrate digital geospatial data together with traditional landform analysis (morphometry) in order to evaluate mechanisms, rates, and modes of surficial process and landscape change;   (5) For specific parts of the Transverse Ranges, Southern Mojave Desert, and Peninsular Ranges, model the four dimensional evolution of basins, mountain fronts, and crustal structure;   (6) Examine the interactive role of climate and tectonics in landscape evolution to see if we can distinguish their respective influences on landscape change;

Project members are conducting geologic mapping in the following areas:

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