Very little quantitative information exists on bedrock hollows and their infilled colluvium. Initial observations in road cuts revealed that the deposits thin upslope. Because the colluvial origin of the fill was not certain, the deposit was termed a "soil wedge" (Dietrich and Dunne 1978). To avoid confusion in usage of the term "soil" we will use here "colluvial wedge," or simply "wedge." Although it is clear that colluvial wedges thin upslope, little else is known about the geometry of the bedrock hollows they occupy, yet this is a very important control on groundwater flow. On soil-mantled hillslopes, rainwater infiltrates rapidly through the soil mantle to underlying and less permeable weathered bedrock. Here water accumulates and travels laterally as shallow groundwater flow, generally following the slope of the bedrock surface (e.g., Campbell, 1975, for further discussion).