We have recently begun to use palinspastic paleogeographic reconstructions as a tool for attempting to identify the structural styles controlling Neogene landscape evolution and sedimentation in the greater Bay area (see Buising and Walker, 1995, reprinted in this volume). We have been particularly interested in assessing the relative roles of strike-slip effects sensu lato and plate boundary-normal contraction in sculpting the Neogene landscapes of the Bay area. The kinematic and temporal relationships between the two structural styles remain largely unclear in the Bay area as in much of the rest of the California Coast Range; resolving this issue in the Bay area has broader applications to addressing the history and significance of compression/contraction along the full length of the Pacific-North American plate boundary.
We currently prefer a version of our paleogeographic reconstructions which suggests that dextral strike slip was the primary control on basin evolution in the Bay area between ~15 Ma and ~6 Ma. Contraction driven by Pacific-North American plate convergence may have become important as early as ~5-7 Ma, somewhat earlier than the date implied by the plate-tectonic datasets of previous workers (e.g., Cox and Engebretson, 1985; Harbert and Cox, 1989). In addition, new structural data from the Rocky Ridge area, Las Trampas 7.5' quadrangle, suggest that in at least parts of the East Bay fold and thrust belt, dextral slip and reverse slip are not discretely partitioned but rather combine to produce oblique slip (see Klinck, this guidebook).
Map with locations of field trip stops
Correlation chart of East Bay Neogene
Stop Four: roadcuts in Cull Canyon
Stop Five:
Rocky Ridge at Las Trampas Regional Park
Field trip leaders were CSUH professor Dr.Anna Buising and graduate students Richard Klinck and Jim Walker