The purpose of the study is to (1) identify the sources of sediment in various environments, (2) define the history and transport processes of the sediments, and (3) better understand the erosion and potential replenishment of the local beaches along the southern coast of the Baja California peninsula. For the purpose of this study, six naturally defined areas were studied separately: El Cardonal, El Arco, San Lucas, El Tiburón, El Tule, and San José. Two main sedimentary provinces were identified via Fourier grain-shape analysis, El Médano and Los Cabos. El Médano sedimentary province includes the El Cardonal and El Arco areas, which are influenced by the dynamics associated with the Pacific Ocean dominated by northwesterly winds, waves, and longshore transport. Beaches from this province have a source mostly from marine material from the shallow shelf, and they are dominantly affected by longshore transport. Secondarily, they are dominated by old and recent aeolian material dissected by intermittent arroyos and local arroyo material from intrusive rocks. The Los Cabos sedimentary province includes the other four areas, and it is influenced by the dynamics of the Gulf of California. In this province, dominant southerly waves are present. Sediment transport occurs along the coast from southwest to northeast; although, some beaches contain material from northern areas, probably related to the direction of waves and sediment transport direction during meteoric events such as hurricanes. Beaches from this province have a source mostly from local arroyo material from intrusive rocks. Other beach material results from longshore transport and some material comes from the El Médano sedimentary province in the El Arco boundary area. Grain-shape data and the information associated with elongation (harmonic 2) show that marine samples (beach, shallow, and deep inner continental shelf) from Los Médanos sedimentary province contain high frequencies of grains with low elongation, opposite of the arroyo samples. This suggests that the low elongation grain source may be farther north of this province. In the Los Cabos sedimentary province, the local arroyos and the longshore transport have been identified as the major factors that nourish and distribute the beach material along the coast. The results of this study parallel those found in similar geographic regions where storms rather than steady currents dominant.

Abstract The Columbia River empties into the Pacific Ocean near latitude 46° N. Much of the detrital load of the river is distributed over a 165 km long littoral cell between Tillamook Head, Oregon, and Point Grenville, Washington. The cell is characterized by north-directed littoral drift in response to dominant southwest winter storms, yet it experiences a summer drift reversal in response to more modest northwest winds and seas. The result has been development of extensive barrier beaches during the late Holocene, which define the major embayments of Willapa Bay and Grays Harbor. The mouth of the Columbia River was modified by jetties beginning late in the nineteenth century. The entrance to Grays Harbor has been jettied since early in the twentieth century. This article discusses changes resulting from these modifications. Dams on the Columbia River and its tributaries built during the twentieth century appear to have significantly reduced the detrital load available to the littoral cell, resulting in the onset of changes in the deposition-erosion regimen.

Abstract The late Wisconsinan and Holocene coastal evolution of southern Lake Michigan contrasts with the coeval history of ocean-coast settings. Multiple transgressive and regressive events occurred, and rates of lake-level change were often greater than the most rapid eustatic sea-level changes. A succession of lower high-lake maxima is recorded in mainland beaches, spits, and beach-ridge/dune complexes across the Chicago/Calumet lacustrine plain. The plain, which extends approximately 120 km from north of Chicago to the Indiana-Michigan border, was the sink for net-southerly littoral transport. During the high-lake phases between 14.5 ka and about 3.5 ka, littoral transport from the eastern and western lake shores terminated in separate spits on opposite ends of the lacustrine plain. Since about 3.5 ka, littoral transport converged along the southern shore. Gradual changes in coastal geomorphology, brought about by littoral processes acting within an overall trend of lake-level decline over the past 2,500 years, formed the modern coastal geography. The Chicago River was transformed from a westward- to an eastward-flowing drainage; littoral-sediment accretion resulted in an extensive beach-ridge/dune complex and a 35-km stream-mouth deflection forming the Grand Calumet River. A model for the coastal sedimentary evolution during the transgressive phases indicates minimal-sediment supply until rate of lake-level change declined and a peak lake level was reached. Wave erosion along the glacial-bluff lake margins could then supply the littoral-transport system. The overall depositional history of the south Lake Michigan coast is that of a regressive and progradational system.