The Mesaverde Formation is one of the major sedimentary deposits in the Rocky Mountain region. In the past few years the Mesaverde section has generated considerable interest as a source of energy resources in the basins of Wyoming, The Upper Cretaceous Mesaverde Formation in the Wind River Basin is a marine, nonmarine. and transitional sequence of sandstones, siltstones. shales and coals. The sedimentation was characterized by pulses of regressions and transgressions resulting in intertonguing of marine and nonmarine deposits. Lenticular sandstones interstratified with shales and coals make correlations and interpretations of interrelationships of the intertonguing units difficult.