MI-23 Aeromagnetic Map of Colorado Download Publication Details This is a state-wide map of the total intensity of earth’s magnetic field in gammas relative to arbitrary datum. This black and white map was produced collaboratively by the USGS and CGS in 1972. Data was compiled across the state from ten total intensity aeromagnetic surveys sourced predominately by the USGS and flown at various heights and spacing. Both magnetic contours and shading are provided on the map. 1 plate (1:500,000). Digital PDF download. MI-23D Citations Zietz, Isidore, and John R. Kirby.Jr. “MI-23 Aeromagnetic Map of Colorado.” Aeromagnetic. Miscellaneous Investigations. Denver, CO: Colorado Geological Survey, Department of Natural Resources, 1972. https://coloradogeologicalsurvey.org/publications/aeromagnetic-map-colorado.