Full Title: FT26CN403. Sedimentary Recycling of High-Pressure Rocks in Subduction Complex Clastic Rocks, Including Mélanges, and Localization of Subduction Interface Slip
Price: US$320 for non-members; US$265 for professional members; US$160 for student members; US$225 for early career professional members
Leader(s): John Wakabayashi; Ron Rubin; David Shimabukuro
Endorser(s): GSA Structural Geology and Tectonics Division; GSA Mineralogy, Geochemistry, Petrology, and Volcanology Division
Industry Track(s): Engineering Geology
CEUs: 2.0
Date(s): Thu.–Sat., 8–10 Oct. 2026
Departing Location: San Francisco International Airport, San Francisco, California, USA
Start Time (first day): 9 a.m.
End Time (last day): 10 a.m.
Description: This three-day trip views mélange and coherent outcrops of the Franciscan Complex in Sonoma County, western California, that bear on the localization of subduction and exhumation slip, sedimentary mixing in mélanges, recycling of previously subducted rocks, and the multiscale architecture of the subduction complex.
Many of the stops feature tourist-worthy scenery. We plan lodging in the Windsor–Healdsburg area. Coastal stops will include Jenner Beach, a fabulous pile of eclogite and garnet blueschist talus at the mouth of the Russian River, and North Shell Beach with exceptional exposures of mélange matrix showing its derivation from conglomerate and an incredible variety of blocks. Inland, we will see outcrops of the Skaggs Springs schist, a coherent quartz-rich blueschist unit, including an outcrop with internal blocks of blueschist-overprinted amphibolite and eclogite along Old Skaggs Springs Road, serpentinite matrix mélange with embedded amphibolite and blueschist blocks along New Skaggs Road.
Near the latter, we will view outcrops of gabbro/quartz diorite of the Coast Range ophiolite. Along the shoreline of Lake Sonoma, we will view blueschist-facies imbricated ocean plate stratigraphy with associated fault rocks, including apparent pseudotachylyte, as well as a >200 m garnet amphibolite block embedded in serpentinite matrix informally nicknamed “The Lord of the Blocks.” Wine tasting at Dry Creek Vineyards and visits to craft breweries, such as Russian River Brewing Company, are planned for those who wish to participate.
Considerations: Some field trip stops will be along roads, whereas others will require short hikes. Suitable hiking clothes and footwear are recommended, along with daypacks and water. One liter of water should be sufficient for even the longest hikes. The longest hike is about 2.5 miles round trip, with approximately 300 feet of elevation gain. Some hiking will be off trail. Poison oak grows in the vicinity of several field trip stops, and ticks and rattlesnakes may be present at some locations.
October weather is expected to be pleasant, but the coastal stops may be cool and the inland stops may be warm. A layered clothing approach is recommended for flexibility, and a hat and sun protection may be useful. The longest drives will occur at the beginning and end of the trip and are anticipated to be about 1.5 hours each. Drives between field trip stops will be shorter (<1 hour). Restroom breaks are planned during both main field days. The third day is devoted to returning rental vehicles to allow for a reasonably early departure to Denver from SFO. A 12:45 p.m. flight from SFO arrives in Denver at 4:28 p.m.
Cost includes lodging, ground transportation, and daily lunch and snacks.
By purchasing this item, you are buying a seat for an in-person geological field trip. This field trip is in conjunction with GSA Connects 2026. Learn more here.
For member type discounts please contact fieldtrip@geosociety.org.
Students and Early Career Professionals can apply for funding here.
Field Trips offer Continuing Education Units (CEUs). One CEU equals 10 hours of participation in an organized continuing education experience under responsible sponsorship, capable direction, and qualified instruction.
Please review these Field Safety Documents. You will be contacted to provide your consent to these forms after purchasing a field trip.
For additional information, please contact fieldtrip@geosociety.org.
Product Code: FT26CN403
Product Category: FTRIP
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