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The San Andreas fault has the highest calculated time-dependent probability for large-magnitude earthquakes in southern California. However, where the fault is multistranded east of the Los Angeles metropolitan area, it has been uncertain which strand has the fastest slip rate and, therefore, which has the highest probability of a destructive earthquake. Reconstruction of offset Pleistocene-Holocene landforms dated using the uranium-thorium soil carbonate and beryllium-10 surface exposure techniques indicates slip rates of 24.1 ± 3 millimeter per year for the San Andreas fault, with 21.6 ± 2 and 2.5 ± 1 millimeters per year for the Mission Creek and Banning strands, respectively. These data establish the Mission Creek strand as the primary fault bounding the Pacific and North American plates at this latitude and imply that 6 to 9 meters of elastic strain has accumulated along the fault since the most recent surface-rupturing earthquake, highlighting the potential for large earthquakes along this strand. 

Modern human behavioral innovations from the Middle Stone Age (MSA) include the earliest indicators of full coastal adaptation evidenced by shell middens, yet many MSA middens remain poorly dated. We apply²³⁰Th/U burial dating to ostrich eggshells (OES) from Ysterfontein 1 (YFT1, Western Cape, South Africa), a stratified MSA shell midden.²³⁰Th/U burial ages of YFT1 OES are relatively precise (median ± 2.7%), consistent with other age constraints, and preserve stratigraphic principles. Bayesian age–depth modeling indicates YFT1 was deposited between 119.9 to 113.1 thousand years ago (ka) (95% CI of model ages), and the entire 3.8 m thick midden may have accumulated within ∼2,300 y. Stable carbon, nitrogen, and oxygen isotopes of OES indicate that during occupation the local environment was dominated by C₃vegetation and was initially significantly wetter than at present but became drier and cooler with time. Integrating archaeological evidence with OES²³⁰Th/U ages and stable isotopes shows the following: 1) YFT1 is the oldest shell midden known, providing minimum constraints on full coastal adaptation by ∼120 ka; 2) despite rapid sea-level drop and other climatic changes during occupation, relative shellfish proportions and sizes remain similar, suggesting adaptive foraging along a changing coastline; 3) the YFT1 lithic technocomplex is similar to other west coast assemblages but distinct from potentially synchronous industries along the southern African coast, suggesting human populations were fragmented between seasonal rainfall zones; and 4) accumulation rates (up to 1.8 m/ka) are much higher than previously observed for dated, stratified MSA middens, implying more intense site occupation akin to Later Stone Age middens. 

Significance Understanding the evolution, dispersals, behaviors, and ecologies of early AfricanHomo sapiensrequires accurate geochronological placement of fossils and artifacts. We introduce open-air occurrences of such remains in sediments of the Middle Awash study area in Ethiopia. We describe the stratigraphic and depositional contexts of our discoveries and demonstrate the effectiveness of recently developed uranium-series dating of ostrich eggshell at validating and bridging across more traditional radioisotopic methods (¹⁴C and⁴⁰Ar/³⁹Ar).Homo sapiensfossils and associated Middle Stone Age artifacts are placed at >158 and ∼96 ka. Later Stone Age occurrences are dated to ∼21 to 24 ka and ∼31 to 32 ka, firmly dating the upper portion of one of the longest records of human evolution. 

Abstract A multiproxy record from a fast‐growing stalagmite reveals variable hydroclimate on the California coast across the 8.2 kyr event and a precursor event likely caused by initial drainage of proglacial Lake Agassiz. Using speleothem δ⁴⁴Ca, we develop the first semiquantitative estimates of paleorainfall variability for California through calibration with measurements of the modern climate and cave environment. We find that the magnitude of rainfall variability during the 8.2 kyr event approached the multiyear variability observable in the recent past (1950–2019) and the magnitude of variability during the precursor event likely exceeded this range. Additionally, we observe other instances of multidecadal variability comparable in magnitude to the precursor event during the record. Our work suggests that speleothem calcium isotope ratios are a powerful semiquantitative means to reconstruct paleorainfall, although numerous factors must be assessed in each cave system before applying this approach.