The King Ridge Road mélange is a unit of the Franciscan Complex, cropping out in an area of at least 50 km 2 around the town of Cazadero, coastal California. This unit is an olistostrome with a massive, unfoliated sandstone matrix, containing >232 large meta-igneous and chert blocks of greatly varying size, lithology, and metamorphic history within the study area. This sandstone matrix is litharenite or arkosic arenite and exhibits prograde prehnite-pumpellyite facies and retrograde zeolite facies metamorphism. It is devoid of megascopic textures except for rare simple bedding. No fossils have been found, and no Bouma units or other graded beds are present. Detrital zircon geochronology has established the maximum age of deposition of the sandstone matrix at 83 Ma, whereas apatite fission-track data indicate cooling of the olistostrome below 100 °C at ca. 35–38 Ma. The 232 exotic blocks sampled in the study area are dominantly low- to medium-grade greenstones and cherts, together with fewer high-grade blocks partly composed of blue amphibole and/or omphacitic pyroxene, and some amphibolites. Thus, many of the blocks have higher grade metamorphic assemblages than the matrix. All block types are well mixed together, so none greatly predominate anywhere. Blocks of oceanic-island-arc plutonic rocks, including granitoids and recemented breccias, are particularly distinctive for this mélange. One granitoid block has a zircon U-Pb age of 165 ± 1 Ma. The massive sandy matrix of the olistostrome formed by accumulation of hyperconcentrated sedimentary density flows (grain flows) sourced primarily from the Klamath-Sierra continental magmatic arc. Many of the blocks record a pre-mélange history of metamorphism and exhumation, followed by partial subduction and reburial with the matrix after 83 Ma. Cooling below 100 °C took place at 35–38 Ma, probably associated with partial exhumation of the unit, with subsequent removal of ~10 km of cover.

Abstract This two-day trip explores the northern San Andreas fault in the Gualala area between Fort Ross and Point Arena (Fig. 1 ). The first stop overlooks the Golden Gate Bridge and includes a discussion of its in-progress seismic retrofit. Several subsequent stops are at paleoseismic sites on the San Andreas fault. The stop at Annapolis Road includes a short hike along the fault through the redwood forest. This section of the fault is locked and has not moved since the 1906 earthquake. Additional stops visit Quaternary marine terraces and include discussion of associated tectonic deformation.

Abstract Contributors: Hans AbramsonWard, Geomatrix Consultants, Inc., 2101 Webster St., Suite 1200, Oakland, California 94612, USA; Julie Bawcom, California Geological Survey, 17501 North Highway 101, Willits, California 95490, USA; John Boatwright, U.S. Geological Survey, 345 Middlefield Rd., M.S. 977, Menlo Park, California 94025, USA; Todd Crampton, Geomatrix Consultants, Inc., 2101 Webster St., Suite 1200, Oakland, California 94612, USA; Wayne Goldberg, City Manager's Office, 100 Santa Rosa Ave., Rm. 10, Santa Rosa, California 95404, USA; Kathryn L.Hanson, Geomatrix Consultants, Inc., 2101 Webster St., Suite 1200, Oakland, California 94612, USA; Victoria E.Langenheim, U.S. Geological Survey, 345 Middlefield Rd., M.S. 989, Menlo Park, California 94025, USA; MortLarsen, Department of Geology, Humboldt State University, 1 Harpst St., Arcata, Cali-fornia 95521, USA; Gaye LeBaron, Press Democrat, P.O. Box 569, Santa Rosa, California 95402, USA; Darcy K.McPhee, U.S. Geological Survey, 345 Middlefield Rd., M.S. 989, Menlo Park, California 94025, USA; William V. McCormick, Kleinfelder, 2240 Northpoint Parkway, Santa Rosa, California 95407, USA; Robert J. McLaughlin, U.S. Geological Survey, 345 Middlefield Rd., M.S. 973, Menlo Park, California 94025, USA; Craig A.McCabe, U.S. Geological Survey, 345 Middlefield Rd., M.S. 973, Menlo Park, California 94025, USA; David P.Schwartz, U.S. Geological Survey, 345 Middlefield Rd., M.S. 977, Menlo Park, California 94025, USA; GarySimpson, SHN Consulting Engineers and Geologists, 812 W. Wabash Ave., Eureka, California 95501, USA; Frank H. (Bert)Swan, Consulting Geologist, 240 Laidley Street, San Francisco, California 94131, USA This guidebook is for a two-day trip: the first part (Day 1) takes place in and near the city of Santa Rosa and on the Rodgers Creek fault in Sonoma County; the second part (Day 2) will go to stops in the town of Willits, on the northern Maacama fault, in Mendocino County. The Rodgers Creek and Maacama faults are major strands of the San Andreas fault system in northern California. The two faults are separated by a right step and may be considered the northern extension of the Hayward and Calaveras faults, which branch from the San Andreas fault south of the San Francisco Bay area (Fig. 1 A). This system of faults accommodates almost a quarter of the total right-slip motion between the Pacific and North American tectonic plates. Slip is released in large, episodic earthquakes and, on some faults, such as the northern Maacama fault, by slow, steady creep.