erc: who: Geodata International what: Aerial Radiometric and Magnetic Survey: Valentine National Topographic Map, Nebraska/South Dakota when: 1981 where: https://digital.library.unt.edu/ark:/67531/metadc1202291/ erc-support: who: University of North Texas Libraries what: Permanent: Stable Content: when: 20081203 where: https://digital.library.unt.edu/ark:/67531/