Geologic and Tectonic Controls on Deep Fracturing, Weathering, and Water Flow in the Central California Coast Range

Abstract

The creation of fractures in bedrock dictates water movement through the critical zone, controlling weathering, vadose zone water storage, and groundwater recharge. However, quantifying connections between fracturing, water flow, and chemical weathering remains challenging because of limited access to the deep critical zone. Here we overcome this challenge by coupling measurements from borehole drilling, groundwater monitoring, and seismic refraction surveys in the central California Coast Range. Our results show that the subsurface is highly fractured, which may be driven by the regional geologic and tectonic setting. The pervasively fractured rock facilitates infiltration of meteoric water down to a water table that aligns with oxidation in exhumed rock cores and is coincident with the adjacent intermittent first‐order stream channel. This work highlights the need to incorporate deep water flow and weathering due to pervasive fracturing into models of catchment water balances and critical zone weathering, especially in tectonically active landscapes.

Aspect Differences in Vegetation Type Drive Higher Evapotranspiration on a Pole‐Facing Slope in a California Oak Savanna

“…However, while the authors describe the landscape as "aspect-regulated with negligible woody-vegetation on EFS," the authors do not include information about the differences in oak tree and grass water uptake. While previous studies in California have suggested that groundwater may sustain oak transpiration when soil water is depleted (Miller et al, 2010), within Arbor Creek Experimental Catchment the winter transient water table at ∼5 m is absent during the summer growing season (Donaldson et al, 2023) and the permanent water table is tens of meters below the land surface (Callahan et al, 2024). Given the lack of groundwater present, this suggests that oak transpiration is likely reliant on unsaturated water storage within weathered bedrock (Hahm et al, 2020(Hahm et al, , 2022.…”