Abstract The architecture of the critical zone—the distribution of mobile regolith, the thickness of weathered rock, and their characteristics, as well as the topography of the land surface—is shaped by erosion and weathering processes that depend upon both lithology and climate. In this trip we explore the Boulder Creek watershed, a landscape that juxtaposes uplifted Precambrian crystalline rocks of Colorado’s Front Range against Mesozoic marine sedimentary rocks underpinning the western edge of the High Plains. The landscape is strongly shaped by Quaternary climate cycles operating on this template inherited from the Laramide orogeny. Stop 1 will provide an overview of the abrupt topographic step at the Front Range–High Plains join, where we will discuss fluvial strath terraces on the Plains. At Stop 2 in Betasso Preserve, we will discuss the impact of the canyon cutting set off by late Cenozoic exhumation of the High Plains on the hillslopes and groundwater systems lining the master stream. At Stop 3, we will hike 2 miles down Gordon Gulch, a focus site in the Boulder Creek Critical Zone Observatory. At stops on the hike, we will discuss exhumation rates, climate-modulated weathering, hillslope hydrology and hillslope sediment transport, and the influence of slope aspect on these processes. Our goal is to focus on the history of climate-driven erosion and weathering processes, and how to incorporate these processes into quantitative models of landscape evolution.

Abstract This field trip highlights gully erosion in the Denver Basin in eastern Colorado. We will explore gully dynamics including: cycles of channel filling and erosion, head-cut migration, and landscape evolution. Research on this site combines observations of modern processes through field instrumentation and a perspective on Quaternary evolution with optically stimulated luminescence dating. Our work at this site has produced insight into the nature of gully erosion. We have found that headcut retreat is controlled by both saturation and drying events, and there is a correlation between the headcut retreat rate and the upstream drainage area. Additionally, through numerical modeling we found that vegetation patterns control long-term gully longitudinal profiles evolution.