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WeJt-developed desert plvements Ire present lbove eolian deposits that mantle noww 01 the CiItUl volcanic rleld, localed in lhe Mojave Desert, California. Soil-straticnphic data ODd geochemical data demonstrate that eolian and pedogenic processes play rn¥x' rotes in the evolution of these pavements. Eolian dust (I) I=leroles mechanical mogmentatloa oIliow rock, providing the source materiaJ for pavements., and (2) accumulates slowly below basaIdc colluvium in Row depressions, eventually promoline development of cumulate loils below the evolving stone pavement. An Increase in dust nux during the Holocene has raised andeaC Pleistocene pavements as much as 20 •cm above the former land surface. The results 01 our studies demonstrate for the first time that most desert pavements do not ronn by deflation, by overland now, or by upw2rd migration of stones through I slowly formed, clayey arcillk horizon.. Desert pavements arc born and maintained at the surfac:e. INTRODUcnON Desen pavements. oonslstmg of • oneto two-panicle.thick layer of closely packed, angu•

We employed a systemwide approach, a large and robust set of radiocarbon ages, and modern process analogs to interpret the Holocene history of forest fire-related sedimentation and overall alluvial activity in northeastern Yellowstone National Park. Debris-flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire-related sedimentation within valley-side alluvial fans of Soda Butte Creek. Fire-related deposits make up approximately 30% of the late Holocene fan alluvium. Fifty 14 C ages on fire-related events cluster within the intervals of 3300 -2900, 2600 -2400, 2200 -1800, and 1400 -800 yr B.P. and suggest earlier episodes of large fires and fan aggradation around 7500, 5500, and 4600 -4000 yr B.P. A major pulse of fire-related debris-flow activity between 950 and 800 yr B.P. coincided with the height of the widely recognized Medieval Warm Period (ca. A.D. 1050 -1200). Instrumental climate records over the last ϳ100 yr in Yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods, enhancing the potential for severe short-term drought, major forest fires, and storm-generated fan deposition. Along lower Soda Butte Creek, fill-cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca. 8000 yr B.P. (terrace level T1a), 7000 -5600 (T1b), 3100 -2600 (T2), 2000 -1300 (T3), and post-800 yr B.P. (T4). These periods coincide with overbank sedimentation on Slough Creek and the Lamar River but alternate with intervals of fire-related fan deposition, implying a strong climatic control. Local paleoclimatic data suggest cooler, effectively wetter conditions during terrace tread formation. In warmer, drier intervals, reduced average runoff in axial streams results in meander-belt narrowing; concurrent channel incision may be caused by infrequent large floods. Greater resistance to downcutting, however, allowed fewer terraces to be formed along Slough Creek and the Lamar River. Alluvial systems in northeastern Yellowstone show a clear response to millennial-scale climatic cycles, wherein alluvial fans aggrade and prograde over flood plains in drier periods. Axial streams widen their flood plains and trim back the fans during wetter periods. ''Smallscale'' climatic fluctuations of the Holocene thus had substantial impact on postglacial landscapes in northeastern Yellowstone.

Radiocarbon dating of late Quaternary deposits and shorelines of Lake Mojave and cation-ratio numerical age dating of stone pavements (Dorn, 1984) on the adjacent Soda Mountains piedmont provide age constraints for alluvial and eolian deposits. These deposits are associated with climatically controlled stands of Lake Mojave during the past 15,000 yr. Six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces, as well as on soil-geomorphic data. All but one of these stratigraphic units were deposited in response to time-transgressive climatic changes beginning approximately 10,000 yr ago. Increased eolian flux rates occurred in response to the lowering of Lake Mojave and a consequent increase in fine-sediment availability. Increased rates of deposition of eolian fines and associated salts influenced pedogenesis, stone-pavement development, and runoff-infiltration relations by (1) enhancing mechanical weathering of fan surfaces and hillslopes and (2) forming clay- and silt-rich surface horizons which decrease infiltration. Changes in alluvial-fan source areas from hillslopes to piedmonts during the Holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less-permeable soils. Inferred increased in early to middle Holocene monsoonal activity resulted in high-magnitude paleo-sheetflood events on older fan pavements; this runoff triggered piedmont dissection which, in turn, caused increased sediment availability along channel walls. Thus, runoff-infiltration changes during the late Quaternary have occurred in response to eolian deposition of fines, pedogenesis, increased sheetflood activity in the Holocene, and vegetational changes which are related to many complicated linkages among climatic change, lake fluctuations, and eolian, hillslope, and alluvial-fan processes.

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