Cordilleran Section

George Morgan, georgemorgan@cox.net; J.R. Morgan; John Prall; Jeff Hull.

Description: This four-day trip will explore the complexity of the Coyote Mountains and exposures there, including Paleozoic to Triassic metamorphic rocks, Nazas Jurassic intrusive units, early Basin and Range extensional structures, ca. 17.9 Ma arrival of Gulf of California during extension, recent faulting, and stream piracy and landslides, etc.

John Platt, Univ. of Southern California, jplatt@usc.edu; Marty Grove, Stanford Univ., mjgrove@stanford.edu; Tarryn Cawood, Univ. of Southern California, cawood@usc.edu.

Description: This three-day pre-meeting trip will examine evidence for successive underplating of metamorphosed oceanic rocks along the Mesozoic convergent margin, with metamorphic grade decreasing from upper amphibolite/eclogite facies to blueschist facies, associated ductile deformation, mélange-type fabrics and extensive metasomatism, and possible signatures of seismic tremor and slow slip in rocks exhumed from >35 km.

Alan Chapman, Macalester College, chapman@macalester.edu; Scott Johnston, Cal Poly San Luis Obispo, scjohnst@calpoly.edu; John Singleton, Colorado State Univ., John.Singleton@colostate.edu; Owen Anfinson, Sonoma State Univ., anfinson@sonoma.edu; Jeremy Hourigan, Univ. of California Santa Cruz, hourigan@ucsc.edu.

Cosponsored by GSA Structural Geologic and Tectonics Division; GSA Geochronology Division; GSA Mineralogy, Geochemistry, Petrology, and Volcanology Division.

Description: This three-day trip will showcase a Mesozoic arc-forearc-trench system exposed along the central California coast that has been dismembered by Late Cretaceous and Neogene tectonism. We will examine the Nacimiento Franciscan complex, forearc basin strata, the Salinian arc, underplated schists, and the Cretaceous–Neogene structures that separate these units.

Jonathan Nourse, Cal Poly Pomona, janourse@cpp.edu; Brian Swanson, California Geological Survey, Brian.Swanson@conservation.ca.gov; Nicolas Barth, Univ. of California Riverside, nic.barth@ucr.edu; Joshua Schwartz, California State Univ. Northridge, joshua.j.schwartz@gmail.com.

Description: This two-day trip examines Paleoproterozoic basement, Neoproterozoic metasedimentary strata, and crosscutting intrusives at Frazier Mountain, Placerita Canyon, and Limerock Canyon and discusses new U-Pb geochronology results bearing on the Proterozoic to Mesozoic history. We will also observe large Late Quaternary landslides sourced from distinct basement rocks in San Antonio Canyon.

Edward Keller, Univ. of California Santa Barbara, keller@ucsb.edu.

Cosponsored by University of California Santa Barbara Earth Research Institute.

Description: One day. The Montecito Debris flow of January 2018 was a wildfire-debris flow–linked event that took 23 lives and damaged or destroyed several hundred homes. This trip will include about six stops to view the 2018 event and two to three older large flows. Social science trip leaders will lead discussions at stops.

Kate Scharer, U.S. Geological Survey, kscharer@usgs.gov; Reed Burgette, New Mexico State Univ., burgette@nmsu.edu; Scott Lindvall, Lettis Consultants International, lindvall@lettisci.com.

Description: One day. The San Gabriel Mountains form the backdrop to Pasadena and are being uplifted along the Central Sierra Madre fault (CSMF). This field trip will visit localities along the CSMF where recent dating reveals the history of fault offset and dynamic aggradation and incision over the past 200 k.y.

Thomas Davis, Geologic Maps Foundation, geologicmapsfoundation@gmail.com; Rick Behl, California State Univ. Long Beach, Richard.Behl@csulb.edu; Katie O’Sullivan, California State Univ. Bakersfield, kosullivan@csub.edu.

Description: This chance-of-a-lifetime four-day trip will traverse the entirety of Santa Cruz Island, one of the few little-disturbed remnants of prehistoric California. We will visit key outcrop- to map-scale structural features (faults and folds) and lovely exposures of the Tertiary stratigraphic succession. Access by 4WD vehicles and hikes (five to six miles).