1. Base of fresh ground water, approximately 3,000 Micromhos, in the Sacramento Valley and Sacramento-San Joaquin Delta, California Author/Creator: Geological Survey (U.S.), cartographer Publication/Creation: Menlo Park, California : Department of the Interior, United States Geological Survey, 1973 Format: Map Access & Availability: Loading
2. Base of principal aquifer for the Elkhorn-Loup model area, North-Central Nebraska Author/Creator: McGuire, Virginia L. Publication/Creation: [Reston, Va.?] : U.S. Dept. of the Interior, U.S. Geological Survey, 2008 Format: Map Edition: Version 1.0. Access & Availability: Loading
3. Base of the upper layer of the phase-three Elkhorn-Loup groundwater-flow model, north-central Nebraska Author/Creator: Stanton, Jennifer S., cartographer Publication/Creation: [Reston, Va.] : U.S. Department of the Interior, U.S. Geological Survey, 2013 Format: Map Access & Availability: Loading