1. Transcontinental geophysical survey (35°-39° N) bouguer gravity map from 87° to 100° W longitude / [cartographic material] Yale Public content 1968. 2012-10-10T14:50:06Z. 2013-03-18T22:22:43Z. Geological Survey (U.S.). Dept. of the Interior, U.S. Geological Survey. English. Public. Middle West and Great Plains.