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The functional dependence of bedrock conversion to soil on the overlying soil depth (the soil production function) has been widely recognized as essential to understanding landscape evolution, but was quantified only recently. Here we report soil production rates for the first time at the base of a retreating escarpment, on the soil-mantled hilly slopes in the upper Bega Valley, southeastern Australia. Concentrations of [sup.10]Be and [sup.26]Al in bedrock from the base of the soil column show that soil production rates decline exponentially with increasing soil depth. These data define a soil production function with a maximum soil production rate of 53 m/m.y. under no soil mantle and a minimum of 7 m/m.y. under 100 cm of soil, thus constraining landscape evolution rates subsequent to escarpment retreat. The form of this function is supported by an inverse linear relationship between topographic curvature and soil depth that also suggests that simple creep does not adequately characterize the hillslope processes. Spatial variation of soil production shows a landscape out of dynamic equilibrium, possibly in response to the propagation of the escarpment through the field area within the past few million years. In addition, we present a method that tests the assumption of locally constant soil depth and lowering rates using concentrations of [sup.10]Be and [sup.26]Al on the surfaces of emergent tors. Keywords: erosion, cosmogenic nuclides, landscape evolution, geomorphology, tors.

The lower part of the Campanian Castlegate Formation, one of the best known fluvial sheet sands of the Western Interior seaway, combines with an overlying finer grained unit (middle member of the Castlegate Formation) to form an unconformity-bounded, third-order stratigraphic sequence (~3 m.y. duration). This sequence contains a mappable muddy zone along the western Book Cliffs of Utah now mapped as contiguous with the open-marine parts of the succession (Buck Tongue, Sego Sandstone, Anchor Mine Tongue) to the east. The correlation within the middle Castlegate has been refined and the nature of the link between tidally influenced fluvial strata in the west and marine strata in the east has been remapped. Five high-frequency stratigraphic sequences (all within the upper part of the larger third-order sequence), forming a thickness to 160 m, have been mapped in the Price area southeastward into the time-equivalent marine succession near Green River. Individual sequences (probably [is less than] 0.5 m.y. duration), reflecting transgressive to regressive estuary infilling, have an internal architecture in which fluvial and tidally influenced distributary-channel belts pass up into muddy central-basin sedimentary units, to bayhead-delta deposits, and in some places up to more fluvial channel belts. The key to the mapping of individual sequences is recognition of the muddy, brackish-water interval, developed during maximum transgression of the time-equivalent shoreline. The two most proximal marine-influenced sequences (2 and 3) are probably broadly time-equivalent with the Buck and Anchor Mine Tongues to the east. The analysis here, contrary to recent suggestions, shows that the marine sequences in the eastern Book Cliffs can be traced far into the time-equivalent, western fluvio-estuarine succession. Keywords: Castlegate, Book Cliffs, nonmarine, sequence stratigraphy.