The maximum extent of Cretaceous onlap is generalized from Plate 3, Structure at the base and subcrop below Mesozoic marine section, Gulf of Mexico Basin (compiled by A. Salvador) in Volume J, The Geology of North America (1991). This dataset contains basic data and interpretations developed and compiled by the U.S. Geological Survey's Framework Studies and Assessment of the Gulf Coast Project. Other major sources of data include publicly available information from state agencies as well as publications of the U.S. Geological Survey and other scientific organizations. In cases where company proprietary data were used to produce various derivatives such as contour surfaces, the source is cited but the data are not displayed.