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Prior work has defined a two-stage history for Yakuno ophiolite petrogenesis consisting of older oceanic basement, and younger island-arc rocks and subordinate elastic rocks. First-stage Yakuno rocks have transitional-type MORB or oceanic plateau affinities, and second-stage Yakuno rocks are more similar to immature island-arc settings. Zircon U-Pb isotopic dates of plagiogranite from the Asago district of Southwest Japan yield crystallization ages of 285 f 2 Ma for the first-stage ophiolite component, and 282 f 2 Ma for the second-stage component of the ophiolite. These results indicate that the two petrologically distinct components of the Yakuno ophiolite in this area formed in a short time interval in the Early Permian. The zircon U-Pb crystallization ages provide a maximum age for the base of the stratigraphically overlying Maizuru Group.

Sedimentary rocks from the (California) State 2–14 research borehole of the Salton Sea Scientific Drilling Project, located in the Imperial Valley of southern California, were deposited in the continental basin of the Salton Trough. Lacustrine shale and siltstone are the dominant lithologies. Sandstones were deposited in lake margin, meander channel fill, and lacustrine delta environments. Framework modal clast compositions of the sandstones indicate a dominant Colorado River provenance. Rare pebbly mudstones were deposited as storm‐induced debris flows. Primary depositional structures in the sediments are commonly disrupted by seismic disturbances. Nonmarine gastropods and ostrocods are relatively uncommon, and occurrences of stratabound sulfides suggest periods of brackish water conditions. Bedded anhydrite and centimeter‐scale mudcracks record intervals of dessication. The State 2–14 sedimentary rocks are interpreted as the basinward facies of the Borrego and Brawley formations which range from Pliocene to Pleistocene in age.