Data on the geosynchronous plasma environment derived from the UCSD plasma detectors on the ATS-5 and ATS-6 satellites have been carefully compiled into a pictorial atlas. The atlas consists of 12 days of data from 1969 (ATS-5), 38 days from 1970 (ATS-5), 37 days from 1974 (ATS-6), and 8 days from 1976 (ATS-6). The data are 10-min averages of the first four moments of the plasma distribution function for the electrons and ions. The data are presented in the form of spectrograms and line plots along with detailed ephemeris and geophysical information. Two computer tapes are available, the formats of which are given in an appendix.