Quartz Valley Geologic Framework and Borehole Data

The Quartz Valley Geologic Framework uses geologic data gathered from previous publications (Mack, 1958) and airborne electromagnetic (AEM) surveys (California Department of Water Resources, 2024) in conjunction with the well log database presented in this data release to create an understanding of the extents and thicknesses of geologic units including channel alluvium, alluvium and basement. Geologic maps and cross sections were taken from a Geological Survey water supply paper (Mack, 1958) to determine surface geologic contacts and general depth to basement material in the valley. Well Completion Reports and AEM data from the California Department of Water Resources (California Department of Water Resources, 2023, 2024) provided lithologic information that was used to determine depth to basement. The well log database includes lithology, well location, depths, construction information, and water levels. These data were interpolated to create the top of basement across the model grid using the three-dimensional modeling program Rockworks, and its inverse distance algorithm for creating grid surfaces. Channel alluvium was added on top of the alluvium layer where current rivers, creeks and ditches are in the valley to be able to add more hydrologic details to the groundwater flow model. This data release includes a shapefile of a grid that defines the extent and thicknesses of the three hydrogeologic layers.