Critical Zone Structure and Landscape Analysis in an Asymmetrical Ridge and Valley System in the Laramie Range, Wyoming

The Earth's surface and subsurface are connected in intricate and complex ways. Variations in factors across Earth's surface such as vegetation distribution, aspect, slope, and water can influence the evolution of the geology 100s of meters beneath the surface. Diverse chemical, physical, hydrological, and biological processes take place near Earth's surface. Together, these processes create a complex system that transforms rock into soil. We sought to understand the connections between deep critical zone (CZ) structure and slope, aspect, and vegetation distribution. We targeted a set of east/west trending ridges with distinct north and south facing slopes and vegetation contrasts that are visible in satellite data in the Laramie Range, Wyoming. Given the sharp contrasts between the north and south facing slopes, we hypothesized that the deep CZ structure would have asymmetrical features. To test our hypothesis, we quantified over 4 kilometers of the deep CZ under two of the three ridges using seismic refraction data. We compared the depth to the base of saprolite (~1200 m/s) and the top of unfractured bedrock (~4000 m/s) against slope, aspect, and canopy height determined by first and last return LiDAR. Despite the large vegetation, slope, and aspect variations at the site, the deep CZ structure showed no asymmetrical patterns. However, we observed thinner (< 15 m) saprolite under locations with the tallest vegetation canopy (> 6 m). In the region, the depth to water is at the bottom of saprolite, meaning thin saprolite allows better access to water. Variabilities in the condition of the fractured rock might also influence the distribution of vegetation, but our findings suggest the correlation between canopy height and saprolite thickness likely highlights a connection between the trees and where water is readily available.